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Water and Environmental Change in the U.S.–Mexico Borderlands

Summary and Keywords

Aridity, a significant characteristic of the U.S.–Mexico borderlands, has affected water use patterns for different groups of people in this region for thousands of years. From indigenous groups to European invaders and colonizers to 20th- and 21st-century farmers, ranchers, and policy-makers in Mexico and the United States, controlling the area’s scarce water resources has been a vital concern for survival and economic success. Given that an international border divides the region, national-era relations between the United States and Mexico often have been marked by water issues and the development of water projects and policies. And on both sides of the border these projects and policies have caused environmental changes that merit attention. Much of that history revolves around agricultural development with the need to ensure steady sources of water for irrigation. But industry and urban areas have also been enormous consumers of scarce water resources in the region, issues that are discussed here.

Keywords: U.S.–Mexico border, borderlands, environment, water use, water policy, water projects, dams, irrigation, ecological change, border cities, water quality

The Border Region

Latin America’s northernmost region is where Mexico and the United States meet, politically at the border, but also where the two countries overlap socially, culturally, and environmentally in the U.S.–Mexico borderlands. Mexico’s northern borderland region, the stretch of land from the Gulf of Mexico to the Pacific Ocean and the nearly 2,000-mile border that separates the country politically from the United States, as well as the states on the U.S. side of the land, rightfully has its own history and historiography. The area encompasses six Mexican border states (Tamaulipas, Nuevo León, Coahuila, Chihuahua, Sonora, and Baja California) and four U.S. states (Texas, New Mexico, Arizona, and California). Until the U.S.–Mexican War, and its resolution with the Treaty of Guadalupe Hidalgo in 1848, those U.S. states, as well as Nevada, Utah, and parts of Wyoming, Colorado, Kansas, and Oklahoma were part of Mexico’s northern provincias internas. Before Mexican control (1821–1848), this vast area of land represented the northernmost reaches of the Spanish Empire in North America, in the viceroyalty of New Spain (1550–1821). During all of these time periods, the region has been, and still is, home to a number of indigenous groups. Thus, in many ways the U.S.–Mexico borderlands represents a hybrid place, a frontier/frontera, or zone of mixed interactions of peoples, cultures, and societies.

One of the most salient characteristics of this borderland region is its aridity. With the exception of the far lower Rio Grande Valley along the easternmost Texas-Tamaulipas border, which receives 23 inches or more of rain a year, the borderlands is remarkably dry, with 10 or fewer inches of annual rainfall. The region’s rivers and the political means of controlling them, then, have been essential for survival and for agricultural and industrial development in the region. As writer and lifetime resident of the Arizona borderlands Charles Bowden put it, “water is energy, and in arid lands it rearranges humans and human ways and human appetites around its flow.”1 Likewise, water supplies have been essential for the development and growth of borderland cities. The water history of the region is tracked here, with emphasis on environmental changes that have taken place over the years as a result of human exploitation of rivers in the U.S.–Mexico borderlands. Controlling the access to water has necessitated policy initiatives and large projects for the construction of dams and reservoirs by both Mexico and the United States. These water control initiatives have required binational agreements and have often generated problems along the border for both nations.

Indigenous Background

Horticultural indigenous groups in this borderland region were the first to develop systems of water supply. Evidence goes back as far as about 700 bce when the Hohokam peoples of the Sonora Desert region in what is today Arizona dug more than 125 miles of irrigation ditches to bring water from the Salt River to their life-supporting crops of maize, beans, and squash (known as the “three sisters”). Their intercropping initiatives, developed by indigenous peoples further south in Mexico centuries earlier, required a seasonal water supply, which the Hohokam engineered using primarily rudimentary wooden digging sticks. Amazingly, some of their canals were thirty feet wide and ten feet deep, and some were lined with a plaster-like substance to avoid ground seepage. Some of their crop fields were on terraced land, meaning that the Hohokam had to design head gates farther upriver to catch the gravity flow that canals could provide to water the higher fields. And they positioned the canals at a gradient severe enough to allow water to flow at a fast rate to avoid evaporation. The Hohokams’ irrigation system was technologically advanced and worked efficiently to support their population for generations without much reliance on meat from hunting.2

By 1000 to 1300 bce the Anasazi peoples of the classic Pueblo culture in what is today northern New Mexico developed a similar irrigation system. At Chaco Canyon archaeologists discovered that the Anasazi built check dams and at least one irrigation ditch more than four miles long to water the essential maize-bean-squash agricultural trio and other crops for food and fiber. Other Puebloan peoples in the upper Rio Grande area also used irrigated, terraced farming techniques, as did the ancestors of the Opata Indians of Casas Grandes in present-day Chihuahua. The irrigation systems amazed Spaniards who entered the region in the 16th century and had never seen anything like them. Many indigenous groups in the region today, such as the Zuñi Pueblo, the Mayo, and the Tohono O’odham, consider water from their homeland rivers to be sacred and continue to practice elaborate religious ceremonies established generations ago honoring and celebrating these waters.3

Other Native peoples in the borderland region were perhaps less technological in their irrigation systems but nonetheless relied on manipulating rivers to support their lifeways. The O’odham of present-day Arizona, for example, did not dig canals but did develop efficient ways to divert water from arroyos (ditches created by heavy rainstorms in the desert’s rainy season) using brush dams to channel water to their crops. They learned to live with the seasons, moving when necessary to follow yearly changes in river flows, eschewing wells for their waters in the belief that digging for groundwater expended too much energy from their communities.4 Further south in Sonora, the Yaqui Indians also practiced floodgate irrigation, using diversion weirs on the Yaqui River to divert water when needed to their agricultural fields. They carefully observed the river’s patterns and even could tell by watching local wildlife when the river would overflow its bank, the optimal time to use the weirs to channel the water to where they needed it. The Yaquis then surrounded the fields with bordos—shallow embankments that held the water to form ponds covering the crops to water them thoroughly. They constructed pole fences from branches to surround the fields as a way to prevent too much debris from floating into the fields. Further from the river, the Yaquis, like the O’odham, made use of seasonal downpours to water fields that were laid out in dry oxbows, or terraces between arroyos and small streams. The Yaquis then diverted water from these waterways by digging ditches at right angles from the arroyos, causing the water to flow into the fields to irrigate their crops. This efficient system has endured for centuries and is still a vital aspect of Yaqui agriculture in southern Sonora.5

These examples of indigenous irrigation and manipulation of water resources are but a part of the larger story of Indian survival and social development in the arid regions of northern Mexico and the southwestern United States. There are many other similar histories of Native adaptation to climate from this part of Latin America. All entail not only long-lasting survival strategies, but also ecological change to local environments. Brush dams, irrigation canals, and diversion weirs all altered the natural course of rivers and streams, modifying vegetation and changing the organic nature of the soil along the way. Croplands, whether in flat valleys or on terraced hillsides, altered local landscapes by introducing plants that would not grow there without intervention by humans and displaced local plant communities that existed there previously, which also interrupted the habitat for local wildlife. Likewise, canals could and did erode into deeper gullies, and sometimes into small canyons, forever changing the landscape and preventing the land from being used for agriculture in the future. That, then, required the breaking in of more land for planting crops. Cycles of environmental change thus continued, causing some groups of Native peoples to regularly search for new lands. The scale of environmental change was, however, mitigated by groups who moved, often allowing a kind of ecological restoration to occur on the land after the semi-nomadic groups moved on.

The European Colonial Era

The scale of environmental change in the region was much greater with the invasion of Spaniards and other Europeans starting in the late 16th century. The European understanding of human-land relationships was significantly different from that of indigenous peoples. Spaniards brought with them to this arid region their own notions and values of water and society, many of which were based on surviving and developing economically in the arid regions of Spain over many centuries. There, both Roman and Arab legacies of water control affected hydrologic sources to irrigate fields and to ensure water supplies for cities. Regulated via a carefully enforced legal system that borrowed from both Roman and Arab traditions, the Spanish system codified policy for establishing water rights, taxes on irrigation water, and the infrastructure to build aqueducts, canals, and other large-scale water projects. Feudal power often came with water resources, and over time, Spaniards viewed and used the control of water in their New World colonies as a source of wealth and power.6

Mexico and its arid northern borderlands proved to be a similar type of place for the Spanish to continue this system. And understandings about water came to symbolize the clash of cultures in the region, as Spaniards believed in water rights and water as a source of wealth and power—concepts foreign to Native peoples of the area. The newcomers believed that they must indeed control water resources, especially with the high evaporation rates characteristic of the region and in a land with so few rivers, most of which only carried seasonally useable flows of water and were dry or shallow for much of the year. In fact, so important was water to the colonial project that it came to dominate Spanish notions of power and law in the borderlands, which often led to conflict with Native groups.7 Spanish missions around the region exerted control over water, while at the same time adapting many indigenous agricultural practices. In the Yaqui Valley, for example, the Jesuits incorporated the Yaqui Indians’ system of floodwater irrigation and expanded it for large-scale wheat production and for introducing livestock into the area. Both enterprises helped to feed a growing population of settlers, but most of the wheat and meat raised were used to support the ever-expanding labor force in the mining frontier of northern Sonora. And both put serious pressure on already scarce water supplies and caused significant environmental change in the area. Converting vast desert areas to irrigated wheat fields and livestock pastures in many ways changed the region’s physical landscape, especially with overgrazing of fields and hoof-action that that was especially damaging to riparian areas.8

For the duration of the colonial period, Spanish legal systems and customs regulated water use in the borderlands. While Spanish law did not always associate property rights automatically with water rights, primarily due to the need for whole communities rather than individual estates to be served by water resources, overall the Spaniards defined water use in terms of land classifications. As such, because most of the land in this region was Crown land—part of the royal patriarchy—water and minerals found there were also considered to belong to the Crown. Domestic uses of water for drinking, cooking, and bathing were not regulated and thus official permissions were not needed for those particular uses. But irrigation for agriculture and livestock and water for industrial uses came under more scrutiny. For example, a grantee of land whose property abutted a water source had to make sure that enough water was reserved for downstream users and could not be denied to neighbors. Irrigated land itself fell into different Spanish classifications thus necessitating Crown policies for acquisition and distribution of water for fields and pastures that was primarily based on the concept of prior use. The policy implied that those who had been given water use rights would not have to fear that those rights would be taken away by other users later. Thus, the Spanish system was not always precise in terms of granting water rights with land rights, which at times led to conflicts between missions or other communities and between land owners themselves. There was a system in place to adjudicate such conflicts and to resolve legal disputes. Parties involved with disagreements over water use rights would call on both priests and the courts to mediate. The legal struggles hid the overarching contests between humans and the natural environment of the arid borderlands. As historian Michael Meyer has written, “Few appreciated that innocent tampering with the delicate desert ecosystem, especially with its natural water reserve, might portend fundamental, permanent change. Legal restrictions on the use of water were defined largely in an ecologically vacuum.”9

The Mexican National Period

The Spanish legal system governing water use carried on into the Mexican national period after independence from Spain in 1810 (actually secured in 1821) and remained relatively unchanged until the U.S.–Mexican War and the cession of about one-third of Mexican land to the United States, when a new border separated the two countries. For the borderlands under study here, during the three centuries from 1550 to 1850 water played a remarkably significant role in regional history. The Spaniards’ increased water use only made the region’s water scarcity worse—a scenario that remained relatively unchanged during Mexico’s early national decades. Two important policies in 19th-century Mexico continued to shape the country’s, and the borderlands region’s, history of water resources. The Treaty of Guadalupe Hidalgo, which ended the U.S.–Mexico War in 1848, included language that mandated that the U.S. government respect the property rights of Mexican residents who now found themselves in U.S. territory. And because under colonial Spanish and early Mexican law water was considered property, Guadalupe Hidalgo required U.S. courts to respect those rights north of the border.10 The border—and the rivers that either formed it or crossed it in various watersheds, became an important dividing line for changes and differences in water use, policies, development, and conservation between the two nations.

The other Mexican policy of importance here was a reworking of the Código Civil of June 1888 that included language on the regulation of the nation’s rivers and water resources. The law, part of the broader nationalistic and dictatorial government of Porfirio Díaz, or the Porfiriato (1876–1911), sought to centralize and make stronger the federal presence in all things related to the economic development of Mexico based on the positivist ideals of Diaz and his technocrat advisers. The law did not exactly make the nation’s rivers and other water resources the property of the state but rather regulated the jurisdiction of the water for both private and public uses. This was important to the Mexican North and borderlands region where diverting rivers for irrigation, and later hydroelectricity, was essential for the fast-paced agricultural development of the region. In the border state of Coahuila, for example, the policy was applied to the Nazas River, which watered the expanding cotton fields of the La Laguna region, to prevent any private conflicting interests for access to and control of the vital waters.11 The Yaqui Valley of Sonora, with its exceptional soil and climate suitable for growing a wide variety of crops, came to be the “breadbasket of Mexico” and the center for export trade during the Porfiriato, especially after Díaz and his technocrats engineered a brutal removal policy against the Yaqui Indians, who had been living and farming there for centuries, to make way for this development project. The same came to be true, although to a lesser degree, in the valleys of the Mayo and Fuerte Rivers in southern Sonora and northern Sinaloa. The region of these three rivers came to be one of the most agriculturally productive in all of North America.12

Much of the development was based on foreign investment, most of which came from private ventures in the United States. American developers worked with Mexican federal and local officials to ensure concessions for water from the rivers with the construction of a network of diversion weirs and canals, often at the expense of indigenous peoples in those valleys who had been using water for their fields for generations. The foreign companies then sold farm plots to North American and European farmers and agri-businessmen who moved to the Yaqui Valley and greatly expanded irrigated agriculture, primarily growing crops for export. Considerable environmental change accompanied these projects, especially in the conversion of thousands and thousands of hectares of fragile desert and dry scrub forest landscapes into agricultural fields. Clearing lands in this kind of arid environment often led to gullying that changed local topographies and hydrologies and retarded the growth of vegetation that would have provided soil cover. As a result, erosion ate away what formerly could have been good farmland. Likewise, local wildlife populations suffered with the loss of natural habitats to agricultural fields, which also affected Native groups in the region who regularly supplemented their diet with the hunting of game animals in the region. Finally, the intense irrigation practiced in Sonora in those years usually did not include adequate drainage from fields. Thus, standing water often caused salinity of the soil, leading to the retirement of thousands of acres from use for agriculture and permanently damaging the soil enough to prevent ecological restoration with native vegetation.13

Water policy in northern Mexico proceeded along those lines into the 20th century, especially as a means to encourage the growth of agriculture, which was a vital aspect of Porfirian developmentalist ideals that encouraged foreign investment and an export-based economy. Such ideals continued apace after the Mexican revolution (1910–1920) that forced Díaz out of office but kept intact, and in fact in many ways accelerated, export industries such as mining and agriculture that required steady flows of water. Starting in the years of President Lázaro Cárdenas (1934–1940) and continuing with the increased infrastructure-minded administration of President Miguel Alemán (1946–1952) after World War II, Mexico launched a nationwide program to harness water resources via a concerted effort to build dams, administered by the Secretaría de Recursos Hidráulicos (SRH) in Mexico City. American developers had pushed for dams on the Yaqui River in order to regulate the flow of water for year-round irrigation purposes. But the first dam in the region, named in honor of President Cárdenas, was not completed until 1942 and was 200 kilometers above the Yaqui Valley. SRH completed a second dam much closer to the valley in 1952, and a third to supply hydroelectric power in 1963. Each dam caused displacement of farm families and entire communities when reservoirs created by the dams inundated up-stream valleys where people lived and farmed. The dams and reservoirs likewise forever changed local environments, changing river flows, creating man-made lakes, and altering the native fauna and flora of the watershed. Similar social and environmental changes occurred on the Fuerte and Mayo Rivers when SRH engineered dams to capture and control their flows of water. Hence, the re-plumbed rivers came to symbolize the power of government to aid agro-industrialists in their quest to increase agricultural production for an international export market.14

The Mexican government built many other dams in Sonora, Chihuahua, and Coahuila that were to benefit farming and ranching interests. Some, like the Abelardo Rodríguez Dam on the Sonora River near the state capital of Hermosillo, never did capture enough water for downstream agri-business. Its reservoir behind the dam today is empty—a low basin where cattle graze on land that was once supposed to be a lake. Thus, downstream agriculture, especially a robust citrus industry, in that part of Sonora and the domestic and industrial water needs of the metropole capital city are dependent on groundwater pumping from the Costa de Hermosillo Aquifer. Irrigation from groundwater is energy-intensive and expensive, and as studies show, the aquifer is fast being depleted without adequate rainfall to keep it at the levels needed for irrigation and urban use.15

On the U.S. Side of the Line and Border Cities

North of the border similar hydro projects got under way to control rivers for irrigated agriculture. And most had similar results of indigenous displacement, disruption of Native lifeways, ecological change, and in some instances, failed reservoirs. In the Arizona borderlands, for example, the U.S. government via the Bureau of Indian Affairs completed the Coolidge Dam on the Gila River in 1928. Like in Sonora, the plan was to guarantee a regulated water flow for downstream farmers, especially for Pima Indians on their Gila River Reservation. But the dam failed to capture sufficient water to be diverted to Pima croplands, the river often runs dry, and the Pimas’ reservation, more barren than ever before, has never become agriculturally prosperous to support the tribe. “Their use of the land is gone,” decries Charles Bowden, “they live on a patch of ground by a dead river.”16

In other ways the Arizona experience is similar to Sonora’s, especially with its history of tapping groundwater. Tucson, like Hermosillo, has come to rely on mining aquifers for urban uses and surrounding agriculture in the Santa Cruz Valley that can grow year-round crops. Because the Santa Cruz River, which flows only seasonally through this region, could never support such high urban and agribusiness water demands, the city started to pump groundwater in 1949. As the urban area continued to grow exponentially in the subsequent decades, aquifer pumping was as high as four times the rate of replenishment and has continued to drop about eight feet a year. The scenario continues to be a political and ecological problem of great magnitude for the city of Tucson, which is currently considering expensive water transfer options to meet current and future water demands.17

Other border cities are facing similar if not worse problems with water. The issues are complicated further for metro urban areas that straddle the line like El Paso/Ciudad Juárez and San Diego/Tijuana because these cities have to deal with supplies of water from rivers or aquifers that are on both sides of the border, and thus are regulated by competing policies. And the border itself has even changed within the Rio Grande, as the island of Chamizal became the center of a border debate between El Paso and Ciudad Juárez, especially when the river’s course changed due to seasonal overflows. The issue was not resolved until the Kennedy administration worked with Mexican authorities in the early 1960s to establish the boundary where it currently is.18 The primary source of water for El Paso and Ciudad Juárez is the Bolsón del Hueco Aquifer, which, because of the exponential population growth of the metro region and its demand for water, is expected to be completely dry by the year 2025 or sooner. A secondary source underneath the border cities is the Bolsón de Mesilla Aquifer, which is also being depleted faster than it is being replenished and will be dry before 2030. The bleak scenario has resulted in conflict between leaders of the twin cities, with those in El Paso criticizing leaders in Ciudad Juárez for failing to plan for water supply diversification, and with the Mexicans responding that Ciudad Juárez has had far fewer resources available, compounded by a staggering and ever-increasing population growth with hundreds of thousands of interior Mexicans flocking to the border city since the late 1990s. Thus, both cities have had to begin drawing on water from the Rio Grande that separates them at the border. Downriver cities east of El Paso rely on the river water for drinking, cooking, and bathing, but only after it has been heavily treated, as the El Paso/Ciudad Juárez metro area dumps an estimated 24,000 gallons of raw sewage a day into the river. This has compounded the problem already present in a region where 12 percent of the border residents do not have access to safe drinking water and are highly susceptible to water-borne diseases. Thus, with water supplies at such a crisis level in this sister city region, officials are exploring the idea of contracting with water suppliers in Canada to have water shipped down by boats tugging “medusa bags” with up to 100,000 cubic meters of water for residents’ use. Such a plan would be exceptionally costly and energy-dependent, but may be one of the few choices left for urban residents in this part of the U.S.–Mexican borderlands.19

On the California–Baja California border, the urban centers of San Diego and Tijuana have experienced similar water crises. Ninety percent of all the people in this borderland area live in these two cities and further east in Calexico/Mexicali, with Tijuana continuing to grow exponentially and expected to double its current population by 2020. For water needs, this demographic trend translated to the San Diego/Tijuana binational zone in 2010 needing 24 percent more water than it did in 1996. Along with domestic use by the cities’ residents, water is in high demand for economic growth through industrial development, for the regional tourist business, and for energy sources, especially for generating electricity at power plants. To power the steam generators and cooling process that produces the electricity to be delivered across the region, the plants operate on a gas turbine combined cycle system that requires 1,000 acre feet of water (or 325.8 million gallons) for every 1,000 megawatts of power produced. Estimates suggest that to continue meeting this high demand for electricity, the power plants will need nearly 81.5 billion gallons of water in an area where drinking water is already scarce. Thus, rivers in the binational urban region have come under enormous pressure. In Baja California, the Tijuana River, and on the California side, the New River and the Colorado River are vital sources of water, with 3.8 trillion liters of water withdrawn from the Colorado a year, which equates to nearly one-quarter of all the drinking water needed for this part of the California borderlands. Ninety-five percent of San Diego’s water comes from the Colorado River or is piped down from northern California. Tijuana has increased its dependency on the Colorado, too, with the construction of an aqueduct that transports water from the river far to the east to Tijuana.20

As in El Paso/Ciudad Juárez, the rivers that serve the Tijuana and San Diego metro areas have become seriously contaminated. Non-point pollution from heavy pesticide and fertilizer use in the intensively agricultural Imperial Valley flows into the Colorado and New Rivers. Hazardous waste and sewage are even greater contaminants. Estimates showed that by the late 1980s the Tijuana River was receiving 76 million liters of raw sewage a day, and the New River about 46 million liters a day. Flow of sewage from the Mexican side of the line into the United States was estimated to be 12 million gallons a day. To address such a significant problem, in 1989 presidents George H. W. Bush and Carlos Salinas de Gortari signed an agreement to establish a binational water treatment facility just north of the border near San Diego to treat sewage from both Tijuana and the south side of San Diego; the United States provided the majority of funding for the project. Further east, the city of Mexicali (capital of Baja California) suffers from a sewage problem with waste dumped into the New River. Not only is contamination a very serious concern, but there are not any new water sources to meet future growth needs of this California/Baja California borderlands region, as interbasin transfers are exceptionally expensive and energy-intensive, although one had been completed in Sonora by 2014 for urban use in Hermosillo.21

The larger Tijuana River watershed and its “landscape diversity” are greatly affected by these disturbances. A basin of more than 4,400 square kilometers, the watershed is characterized by riparian vegetation and grasslands that are home to the Kumiai Indians. The urban development in the region and its use of water from the Tijuana River have been the principal cause of environmental change. The changes are reflected in considerable habitat loss for wildlife and the destruction of land used for agriculture and gathering by the Kumiai people.22 A border water project at the University of California–San Diego is working to address these problems but has found that water availability is constrained more by political than technological issues. Water in the arid borderlands of this urban zone will always pose significant challenges, especially with increased population pressures.23

Borderlands Rivers

As the University of California–San Diego study further argues, policies are what have dictated water availability and control in many ways. In the U.S.–Mexico Borderlands, the policies are from both countries and binational. In fact, all surface water in the region (but not underground aquifers) is allocated to various users by international treaties.24 The first such treaty between the two nations, and the one that many scholars consider to be the policy that would serve as a precedent for others, was the 1906 Water Convention that—twenty years in the making—apportioned water from the Rio Grande. One of its objectives was to ensure water for Ciudad Juárez, but the United States benefited the most from the treaty, securing roughly a 10 to 1 ratio of the river’s resources for the U.S. consumers. This was especially important for downstream users in the lower Rio Grande Valley who had established a thriving agricultural industry, based primarily on citrus crops and truck farms. The convention dealt only with the upper Rio Grande and did not affect the lower reaches of the river nor did it deal with the Colorado River on the Arizona-Sonora border.25 The Colorado River came to be governed by a 1922 unilateral, six-state pact between upstream providers (Wyoming, Utah, Colorado, and New Mexico) and downstream users (Arizona, California). The Colorado River Compact guaranteed the downstream states an average of 7.5 million acre-feet of water a year over a ten-year period. Agricultural interests in the Mexican states of Sonora and Baja California also relied on the Colorado River, as the river’s mouth is in Mexico, where it dumps into the Sea of Cortez just below Arizona. But there were no Mexican delegates at the 1922 meetings that hammered out the compact, and thus Sonoran and Baja farmers were slighted on having access to water until their concerns were addressed in 1944.26

Many aspects of the Colorado River Compact had significant impacts on Mexico. First, the compact enabled a steady flow of water for agricultural and urban interests in Arizona and California, while the upstream states were guaranteed adequate water for their own uses. To meet both of these ends the states agreed on the construction of a series of water storage facilities (dams and reservoirs) to facilitate reclamation of water resources while at the same time providing a steady, predictable flow of water to the downstream users. From the 1930s to the 1970s a flurry of reclamation projects were undertaken, including such monumental ones as Hoover Dam and the Glen Canyon Dam, and such water delivery systems downstream as the All American Canal in California, which created the Imperial Valley, and the Central Arizona Project that created a canal to water the industrial agricultural interests of that state. All diverted water away from the river before it ended its journey across the border in Mexico, leaving very little for Sonoran and Baja users. In fact, the Colorado River was often dry as it crossed the border. The Imperial Valley thus flourished as a zone to grow year-round crops.27 Over the years the All American Canal has radically changed the environment on both sides of the border, with transformation of the desert lands in both the Imperial and Mexicali Valleys, affecting the local watershed. The 1922 compact had no provisions to address water quality. But stored water in reservoirs in the arid heat of the American Southwest evaporated quickly and often became sterile with salinization. By 1961 the downstream quality of the water was so degenerated that what little crossed the border was often useless for irrigation in northern Mexico.28

But what guaranteed Mexico what water it got from the Colorado River was the result of a far more important binational treaty than the one between the United States and Mexico in 1906. Forty years later, the Mexican government pushed for a policy that would govern the border water resources, namely the Rio Grande (called the Rio Bravo del Norte in Mexico) and the Colorado River.29 What resulted was the 1944 Water Treaty that brought Texas, California, and Mexico together to establish the framework for sharing water from these important rivers. Sometimes known as the “Law of the River,” the 1944 treaty guaranteed 350,000 acre-feet of Rio Grande below the Conchos River to the United States in exchange for guaranteeing Mexico 1.5 million acre-feet of water annually from the Colorado River. The 1944 treaty was the result of a long-standing disagreement over Colorado River water for agricultural use in Sonora and Baja California. Mexican President Manuel Ávila Camacho desired an end to the crisis and by 1941 had initiated talks to resolve the issue. On the U.S. side, the Office of Inter-American Affairs (OIAA)—an entity headed by Nelson Rockefeller to improve relations, especially cultural ones, between the United States and Latin America under the mandate of President Franklin Roosevelt’s Good Neighbor Policy—was involved. The United States was keen on securing Mexico as an ally during World War II and thus wanted to solve conflicts that could adversely affect that relationship. The OIAA found that northern Mexico’s irrigation needs had expanded substantially and that farmers in the region were desperate for Colorado River water. The California agri-industry lobbied strongly against the treaty’s passage, claiming it would divert too much water away from the Imperial Valley, but in February 1944 both the U.S. and Mexican governments signed the treaty, and the U.S. Senate ratified it later that year.30

The treaty provided for the construction of common dams and diversion canals for the two countries. Priorities included municipal, industrial, and agricultural development, hydropower projects, and the establishment of the International Boundary and Water Commission (IBWC) to manage the treaty and monitor border “sanitation” issues, although there were no measures for effective pollution monitoring or enforcement in the treaty. Sanitation at that time concerned wastewater treatment facilities, and the IBWC did oversee the development of one for the twin Nogales cities on the Arizona-Sonora border in the 1950s. The primary purpose of the IBWC was to develop necessary public works for the successful withdrawal of water from the Rio Grande and Colorado River within the limits set by the treaty, mainly by the construction of dams to maximize water availability.31 The dams themselves were extremely damaging to natural systems in their environs and to downstream flows. Creating steady water supplies and regular releases via floodgates and release valves altered the seasonal flood patterns on which downstream Colorado River environments depended, especially by allowing the growth of exotic species like tamarisk that choke out riparian vegetation that otherwise would be swept out with the seasonal flooding. The new regime is artificial and unhealthy to stream corridors and river health. Moreover, salinity increases dramatically with stored water in arid climates and from water sitting in irrigation ditches, causing downstream havoc with local populations dependent on the river water for agriculture and domestic needs. Attempts to restore natural flood regimes are massive and expensive, usually requiring removal of the water control structures—unpopular prospects with policy makers and legislators in states that benefit economically from downstream irrigation.32

Environmental Considerations

Since 1944 there have been so many vast changes to the borderlands region that water availability has certainly not stayed as consistent as hoped for by the treaty proponents. Long-lasting droughts, incredible population growth, increased industrialization with the development of the Border Industrial Zone first in the 1960s and later maquiladoras (assembly plants) and depletion of groundwater sources have all put far more pressures on the Rio Grande and the Colorado River since passage of the Water Treaty.33 Thus, in 1968 the U.S. government beefed up its commitment to Mexico to guarantee the water it deserved with the Colorado River Basin Project Act. This shifted the burden from the six-state compact to the federal government to deliver water of “reasonable quality” to the Mexicans.34 In 1974, the U.S. Congress acted again, this time to address the issue of heavily saline water from the Colorado River that was entering Mexico. The Colorado River Basin Salinity Control Act of that year provided for upstream salt-control measures in Nevada, Utah, and Colorado, and for the construction of what would become one of the world’s largest desalinization plants at Yuma, Arizona.35 In 1983 the governments of the United States and Mexico, under presidents Ronald Reagan and Miguel de la Madrid, pounded out yet another binational treaty. This one, named the Border Environmental Cooperation Agreement (often referred to as the La Paz Agreement), had more authority than did the International Boundary and Water Commission, although it dealt with other border environmental problems than just those related to water. It called on the two nations to consult and exchange information on environmental issues on a regular basis, and it established binational committees to address water and air pollution and hazardous materials, and to have included in such discussions and decision-making the voices of state, local, and tribal governments and nongovernmental environmental organizations. It was this policy that enabled the development of the binational sewage treatment plant south of San Diego and that addressed similar contamination and pollution problems in the U.S.–Mexican borderlands.36

But a decade later the situation had only become worse. Northern Mexico’s maquiladora industry by then had overwhelmed the scant water supplies, treatment facilities, and waste disposal systems in the border cities. Settlers from interior Mexico flocked to the borderlands on both sides, with no other place to live than cheaply built colonias (shantytowns) with inadequate drinking water supplies or sewage. Once again leaders from both nations met and established the Border Environment Cooperation Commission (BECC) along with the North American Development Bank to help finance the construction of water facilities and wastewater and sewage systems along the border.37 BECC was part of the broader tri-national North American Free Trade Agreement (NAFTA) and a response to robust criticisms that emerged with the free trade program’s initial lack of emphasis on border environmental concerns. It was accompanied by other alphabet commissions, such as Integrated Border Environmental Plan (IBEP, 1992) and the North American Agreement for Environmental Cooperation (1993), with its implementation arm the Commission for Environmental Cooperation (CEC), all of which have worked to study water availability and quality, sanitation, and pollution in the U.S.–Mexico borderlands region.38 NAFTA’s support for economic growth has meant a surge in industrial development along the border, all with impacts on water availability and quality. More research will be needed to assess the success of the BECC, IBEP, and CEC in dealing with water-related environmental problems on the border. But since their inception they have been constrained by funding problems, limited resources, and political disinterest from both the United States and Mexico.39


From prehistoric times to the present, water, its scarcity and its use, has been one of the most important concerns of the region we know today as the U.S.–Mexican borderlands. Development, population growth, agriculture, industry, and the rise of cities have all put pressure on what is inherently an arid region. With such diverse threats to a scarce resource from both the United States and Mexico, it is no surprise that there has been so much attention to binational policies that have helped shape the course of water in the region. The environmental changes associated with this historical trajectory are logical outcomes of such water manipulation schemes and programs. And that scenario will persist as humans continue to live and develop economically in the borderlands region.

Discussion of the Literature

The seminal work on water in the borderlands is Michael Meyer’s Water in the Hispanic Southwest, and it continues to be used, cited, and referenced across a broad spectrum of disciplines, especially in history and geography. It is a fine example of both legal and social history from the Spanish colonial era to the mid-19th century. And while Meyer was not an environmental historian, there is a great deal of environmental history in his book, especially with his discussion of “ecoculturation.”40 For histories that push the discussion of water in the region into the 20th and 21st centuries, including discussion of binational policies that have affected water supplies on both sides of the U.S.–Mexican border, the standard works by Norris Hundley Jr., Philip Fradkin, Stephen Mumme, Evan Ward, Douglas Littlefield, and April Summitt, edited by Gary Weatherford and Lee Brown, and the work of Fred Phillips, Emlen Hall, and Mary Black remain very important.41 An important newer shift to understand water in the region is to look past rivers and watersheds and explore underground aquifers. The most important work on that topic is José Luis Moreno’s Por abajo del agua. And as mentioned, important new insights are being published on water pollution in the borderlands.42 All of these topics will be themes for many more years, as aridity, water, and water policy all combine to form some common and some different histories to tell on both sides of the U.S.–Mexico border.

Primary Sources

There are several excellent resources available to students and scholars for researching the water history of the Southwest borderlands. The best place to start would be in Tucson at the University of Arizona’s Special Collections department at the main library. It has archived there the papers of the Richardson Construction Company (which began the irrigation schemes in the Yaqui Valley of Sonora), a large array of borderlands maps, a great deal of material on indigenous Arizona and Sonora, and other materials on more recent water treaties between Mexico and the United States. Also in the Special Collections are the Stewart Udall Papers, which contain significant files on western water, the Central Arizona Project, and the Mexican Water Treaty, as well as primary sources on providing the cities of Phoenix and Tucson with water. The Morris K. Udall Papers there also contain valuable primary documents regarding the Central Arizona Project. The library also has the entire collection of Irrigación en Mexico—a periodical of Mexico’s water project and irrigation bureaucracy that is an excellent resource to track the development of large-scale hydro projects throughout Mexico, including those in the borderlands region. The Nettie Benson Latin American Collection at the University of Texas in Austin has a wide array of materials on the Rio Grande borderlands. In Mexico, the Archivo General del Estado de Sonora (AGES) in Hermosillo, Sonora, is home to the most extensive collections of Sonoran records, including those on water (although the cataloguing of materials remains rather archaic there). One could check other state agencies involved with water policy, but they do not have historical documents. The best collections for historical materials on water history for all of Mexico are at the Archivo Histórico de Agua (AHA) in Mexico City. Using its computer-based catalogue, one can search for materials on borderlands water projects in Mexico’s North. Finally for borderlands water and environmental policies related to NAFTA and other treaties, students should be encouraged to check the website of the Commission for Environmental Cooperation.

Further Reading

Andrés, Benny J. Power and Control in the Imperial Valley: Nature, Agribusiness, and Workers on the California Borderland, 19001940. College Station: Texas A&M University Press, 2014.Find this resource:

    Bergman, Charles. Red Delta: Fighting for Life at the End of the Colorado River. Golden, CO: Fulcrum, 2002.Find this resource:

      Bowden, Charles. Killing the Hidden Waters: The Slow Destruction of Water Resources in the American Southwest. Austin: University of Texas Press, 1977.Find this resource:

        Evans, Sterling. “Yaquis vs. Yanquis: An Environmental and Historical Comparison of Coping with Aridity in Southern Sonora,” Journal of the Southwest 40.3 (Autumn 1998): 363–396.Find this resource:

          Fradkin, Philip L. A River No More: The Colorado River and the West. New York: Alfred A. Knopf, 1981.Find this resource:

            Hundley, Norris, Jr. Dividing the Waters: A Century of Controversy between the United States and Mexico. Berkeley: University of California Press, 1966.Find this resource:

              Littlefield, Douglas. Conflict on the Rio Grande: Water and Law, 18791939. Norman: University of Oklahoma Press, 2008.Find this resource:

                Meyer, Michael C. Water in the Hispanic Southwest: A Social and Legal History, 15501850. Tucson: University of Arizona Press, 1984.Find this resource:

                  Moreno Vázquez, José Luis. Por abajo del agua: Sobreexplotación y agotamiento del acuífero de la Costa de Hermosillo, 19452005. Hermosillo, Mexico: Colegio de Sonora, 2006.Find this resource:

                    Mumme, Stephen P. “Engineering Diplomacy: The Evolving Role of the International Boundary and Water Commission in U.S.–Mexico Water Management,” Journal of Borderland Studies 1.1 (Spring 1986): 73–108.Find this resource:

                      Phillips, Fred M., G. Emlen Hall, and Mary E. Black. Reining in the Rio Grande: People, Land, and Water. Albuquerque: University of New Mexico Press, 2011.Find this resource:

                        Summitt, April R. Contested Waters: An Environmental History of the Colorado River. Boulder: University Press of Colorado, 2013.Find this resource:

                          Ward, Evan. Border Oasis: Water and the Political Ecology of the Colorado River Delta, 1940–1975. Tucson: University of Arizona Press, 2003.Find this resource:

                            Weatherford, Gary D., and F. Lee Brown, eds. New Courses for the Colorado River: Major Issues for the Next Century. Albuquerque: University of New Mexico Press, 1983.Find this resource:

                              Worster, Donald. Rivers of Empire: Water, Aridity, and the Growth of the American West. New York: Oxford University Press, 1985.Find this resource:


                                (1.) Charles Bowden, Killing the Hidden Waters: The Slow Destruction of Water Resources in the American Southwest (Austin: University of Texas Press, 1977), 7.

                                (2.) Michael C. Meyer, Water in the Hispanic Southwest: A Social and Legal History (Tucson: University of Arizona Press), 11–12.

                                (3.) Ibid., 12, 15. For more on Puebloan culture and water use in New Mexico, see Fred M. Phillips, G. Emlen Hall, and Mary E. Black, Reining in the Rio Grande: People, Land, and Water (Albuquerque: University of New Mexico Press, 2011), chapter 2.

                                (4.) Bowden, Killing the Hidden Waters, 6–7.

                                (5.) Meyer, Water in the Hispanic Southwest, 11; Sterling Evans, “Yaquis vs. Yanquis: An Environmental and Historical Comparison of Coping with Aridity in Southern Sonora,” Journal of the Southwest 40 (Autumn 1998): 373.

                                (6.) Meyer, Water in the Hispanic Southwest, 19–21.

                                (7.) Ibid., 20–23.

                                (8.) Evans, “Yaquis vs. Yanquis,” 374.

                                (9.) See Meyer, Water in the Hispanic Southwest, especially chapters 5 and 6 on the Spanish legal system as it applied to water rights. Quotation is from p. 166.

                                (10.) Ibid., 166–167; and Michael M. Brescia and John C. Super, North America: An Introduction (Toronto: University of Toronto Press, 2009), 43.

                                (11.) Luis Aboites, El agua de la nación (18861946) (Mexico City, Mexico: CIESAS, 1997), 82–86.

                                (12.) Evans, “Yaquis vs. Yanquis,” 378–381; and Brescia and Super, North America, 43.

                                (13.) Evans, “Yaquis vs. Yanquis,” 379–381, 386–387.

                                (14.) See Sterling Evans, “La angustia de La Angostura: Consequencias socio-ambientales por la construcción de presas en Sonora,” Signos Históricos 16 (julio-diciembre 2006), 46–78. For more on agriculture and water in general for the state of Sonora, see Sociedad Sonorense de Historia, ed., El agua y la agricultura en la historia de Sonora (Hermosillo, Mexico: Sociedad Sonorense de Historia, 2004).

                                (15.) See José Luis Moreno Vásquz, Por abajo del agua: Sobreexplotación y agotamiento del acuífero de la Costa de Hermosillo, 19452005 (Hermosillo, Mexico: Colegio de Sonora, 2006).

                                (16.) Bowden, Killing the Hidden Waters, 86–87. Quotation is on p. 87.

                                (17.) Ibid., 123–125.

                                (18.) See Jeffrey M. Schultze, “The Chamizal Blues: El Paso, the Wayward River, and the People Inbetween,” Western Historical Quarterly 43 (Autumn 2012): 301–324.

                                (19.) Fernando Romero and LAR, Hyper-Border: The Contemporary U.S.–Mexico Border and Its Future (New York: Princeton Architectural Press, 2008), 96–97, 235, 247–249, 274. See also, Paul Ganster, “The United States–Mexico Border Region and Growing Transborder Interdependence,” in Stephen J. Randall and Herman W. Konrad, eds. NAFTA in Transition (Calgary, AB: University of Calgary Press, 1995), 164. Medusa bags are like giant bladders that contain thousands and thousand of gallons of water and can be floated down rivers and along ocean coasts.

                                (20.) Romero and LAR, Hyper-Border, 269, 235–236, 274; and Ganster, “The United States–Mexico Border Region and Growing Transborder Interdependence,” 164, 166.

                                (21.) Ganster, “The United States–Mexico Border Region and Growing Transborder Interdependence,” 165–166; and Romero and LAR, Hyper-Border, 274.

                                (22.) Linia Ojeda Revah, “Land Use and the Conservation of Natural Resources in the Tijuana River Basin,” in Lawrence A. Herzog, ed. Shared Space: Rethinking the U.S.–Mexico Border Environment (La Jolla, CA: Center for U.S.–Mexican Studies, 2000), 212–215, 227, 230.

                                (23.) Romero and LAR, Hyper-Border, 245.

                                (24.) Ganster, “The United States–Mexico Border Region and Growing Transborder Interdependence,” 164.

                                (25.) Stephen P. Mumme, “The Liquid Frontier: Water and Sustainable Development on the U.S.–Mexico Border,” Journal of the West 47 (Summer 2008): 56.

                                (26.) David H. Getches and Charles J. Meyers, “The River of Controversy: Persistent Issues,” in Gary D. Weatherford and F. Lee Brown, eds. New Courses for the Colorado River: Major Issues for the Next Century (Albuquerque: University of New Mexico Press, 1983), 55. For more on the six-state compact, see Norris Hundley Jr., Dividing the Waters: A Century of Controversy between the United States and Mexico (Berkeley: University of California Press, 1966); Donald Worster, Rivers of Empire: Water, Aridity, and the Growth of the American West (New York: Oxford University Press, 1985); Donald J. Pisani, To Reclaim a Divided West: Water, Law, and Public Policy, 18481902 (Albuquerque: University of New Mexico Press, 1992); Phillip L. Fradkin, A River No More: The Colorado River and the West (New York: Alfred S. Knopf, 1981); Marc Reisner, Cadillac Desert: The American West and Its Disappearing Water (New York: Penguin Books, 1986); and Evan Ward, Border Oasis: Water and the Political Ecology of the Colorado Delta, 19401975 (Tucson: University of Arizona Press, 2003). For more on the impacts at the mouth of the Colorado River in Mexico, see Charles Bergman, Red Delta: Fighting for Life at the End of the Colorado River (Golden, CO: Fulcrum, 2002).

                                (27.) See Ward, Border Oasis; Worster, Rivers of Empire; Hundley, Dividing the Waters; Reisner, Cadillac Desert; Fradkin, A River No More; April R. Summitt, Contested Waters: An Environmental History of the Colorado River (Boulder: University Press of Colorado, 2013); Bergman, Red Delta; and Benny Andrés, Power and Control in the Imperial Valley: Nature, Agribusiness, and Workers on the California Borderland, 1900–1940 (College Station: Texas A&M University Press, 2014).

                                (28.) Romero and LAR, Hyper-Border, 247; and Getches and Meyers, “River of Controversy,” 68.

                                (29.) For complete discussion of legal aspects of the Rio Grande prior to the 1944 treaty, see Douglas Littlefield, Conflict on the Rio Grande: Water and the Law, 18791939 (Norman: University of Oklahoma Press, 2008); and Phillips, Hall, and Black, Reining in the Rio Grande.

                                (30.) Mumme, “The Liquid Frontier,” 56–57; and Rankin, ¡México, la Patria!: Propaganda and Production during World War II (Lincoln: University of Nebraska Press, 2009), 204–205.

                                (31.) Mumme, “The Liquid Frontier,” 56–57; John H. Knox, “The CEC and Transboundary Pollution,” in David L. Markel and John H. Knox, eds. Greening NAFTA: The North American Commission for Environmental Cooperation (Stanford, CA: Stanford University Press, 2003), 81. For more detailed discussion of the IBWC, see Stephen P. Mumme, “Engineering Diplomacy: The Evolving Role of the International Boundary and Water Commission in U.S.–Mexico Water Management,” Journal of Borderland Studies 1 (Spring 1986): 73–108.

                                (32.) Daniel J. Simberloff, et al., “Regional and Continental Restoration,” in Michael E. Soulé and John Terborgh, eds. Continental Conservation: Scientific Foundations of Regional Reserve Networks (Washington, DC: Island Press, 1999), 89.

                                (33.) Romero and LAR, Hyper-Border, 245; and Knox, “The CEC and Transboundary Pollution,” 82.

                                (34.) Helen M. Ingram, Lawrence A. Scaff, and Leslie Silko, “Replacing Confusion with Equity: Alternatives for Water Policy in the Colorado River Basin,” in Weatherford and Brown, eds. New Courses for the Colorado River, 193.

                                (35.) Norris Hundley, Jr., “The West against Itself: The Colorado River—An Institutional History,” in Weatherford and Brown, eds. New Courses for the Colorado River, 39.

                                (36.) Ganster, “The United States–Mexico Border Region and Growing Transborder Interdependence,” 168–169; and Mumme, “The Liquid Frontier,” 59.

                                (37.) Knox, “The CEC and Transboundary Pollution,” 83.

                                (38.) Mumme, “The Liquid Frontier,” 60.

                                (39.) Carolyn L. Deere and Daniel C. Esty, “Trade and Environment: Reflections on the NAFTA and Recommendations for the Americas,” in Carolyn L. Deere and Daniel C. Esty, eds. Greening the Americas: NAFTA’s Lessons for Hemispheric Trade (Cambridge, MA: MIT Press, 2002), 338–339.

                                (40.) Meyer, Water in the Hispanic Southwest.

                                (41.) Hundley Jr., Dividing the Waters; Mumme, “Engineering Diplomacy” and “The Liquid Frontier”; Ward, Border Oasis; Littlefield, Conflict on the Rio Grande; Summitt, Contested Waters; Weatherford and Brown, eds., New Courses for the Colorado River; and Phillips, Hall, and Black, Reining in the Rio Grande.

                                (42.) See, for example, Ojeda Riva, “Land Use and Conservation of Natural Resources in the Tijuana River Basin”; Knox, “The CEC and Transboundary Pollution”; Romero and LAR, Hyper-Border; and Deere and Esty, Trade and Environment.