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As officials from the Colorado River Basin States (AZ, CA, CO, NM, NV, UT and WY) and the U.S. Bureau of Reclamation (USBR) struggle to reach consensus on how to manage the declining river after 2026 when current agreements expire, some things remain clear. 

First, Colorado River water usage exceeds supply, evident in the continued decline of the Colorado River’s reservoirs that were full 25 years ago. Today, they sit two-thirds empty. 

Second, solutions are urgently needed. Nearly 40 million people depend on the Colorado River water supply, and 400 bird species depend on the Colorado River’s habitats.  Water needs across the basin must be met without harming the last remaining Colorado River-dependent habitats, including the Ciénega de Santa Clara in Sonora, Mexico. 

Unfortunately, some water users are reviving interest in restarting the Yuma Desalting Plant, an antiquated U.S. facility in southwestern Arizona that, if operated, would negatively impact essential bird habitat. 

Earlier this month, the board of the Central Arizona Water Conservation District (the agency that manages the Central Arizona Project, the 336-mile long canal that delivers Colorado River water to central and southern Arizona) proposed a measure to support operation of the Yuma Desalting Plant, specifically calling on the federal government to prioritize reducing “the impact of the bypass flows on the Colorado River system.” This obscure mention of “bypass flows” is a direct reference to the water that supplies the Ciénega de Santa Clara, the largest remaining wetland in the long-desiccated Colorado River Delta. Extracting water from this ecosystem could have devastating impacts on the natural heritage and wildlife of the Colorado River Basin and could extend to the migrating birds of the Pacific Flyway. 

As ̽����ѡ implements Flight Plan—our strategy to conserve 300 million acres of quality, connected, and climate-resilient habitat—protecting and restoring bird habitats while improving the health and reliability of our water supplies for communities is a priority for our Colorado River program.
 
Origins of the Ciénega de Santa Clara

The Ciénega provides crucial habitat, food, and shelter for hundreds of thousands of birds who migrate north and south along the Pacific Flyway, including the Western Sandpiper, American Avocet, and Snowy Plover. It also supports the world’s largest remaining population of the endangered Yuma Ridgway’s Rail, a reclusive bird living in the marshes. 

In 1972, in the wake of adopting water quality standards for Colorado River water deliveries to Mexico, the United States worked with Mexico to build a canal (called the Main Outlet Drain Extension, or “MODE”) to divert salty agricultural drainage water from the Wellton-Mohawk Irrigation and Drainage District in southern Arizona away from the Colorado River. This canal diverted the water supplies away from the river because farms downriver in Mexico’s Mexicali Valley had been experiencing damage to their salt-sensitive crops. The salty water in the MODE canal is known as the “bypass flow” because it bypasses the Colorado River. 

For more than 40 years, the “bypass flow” of approximately 100,000 acre-feet of salty water has flowed in the MODE canal, emptying east of the Colorado River into the mudflats of the former Colorado River Delta and creating the Ciénega de Santa Clara. In the context of the Colorado River Delta, where nearly 2 million acres of wetland habitat disappeared as the Colorado River was dammed and diverted over the last century, the Ciénega is the largest remaining wetland. 

At more than 44,500 acres, this essential wetland includes:

• Cattail marshes that filter water, stabilize sediments, and offer cover for wildlife
• Open water areas that nourish fish populations, provide resting areas for waterfowl, and maintain hydrological connections
• Mud flats that serve as important feeding grounds for shorebirds and wading birds, supporting rich invertebrate prey 

Mexico recognizes the Ciénega de Santa Clara’s importance, and in 1993, along with the United Nations Educational, Scientific, and Cultural Organization (UNESCO) designated the Ciénega as a Biosphere Reserve. In 1997, the Ciénega was designated a Ramsar Convention Wetland of International Importance. 

̽����ѡ’s own science repeatedly documents the outsized importance of the Colorado River Delta—particularly the Ciénega—for birds.

Problems with the Yuma Desalting Plant 

The Yuma Desalting Plant, an antiquated facility in southwestern Arizona, was built between 1975 and 1992 to treat the salty “bypass flow” so it could be returned to the Colorado River and sent to Mexico. The plant operated only briefly in 1993 before it was damaged by floods and since then has mostly sat dormant. Restarting the plant would have significant impacts.

Operation at just one-third of the Yuma Desalting Plant’s capacity would divert approximately 25 percent of the bypass flow currently sustaining the Ciénega, while disposing high-salinity brine concentrate into the MODE canal, significantly diminishing both the quantity and quality of water flowing to the Cienega threatening the ecosystem with collapse and putting hundreds of thousands of birds at risk. 

Bringing the Yuma Desalting Plant back into regular operation at just one-third of its full capacity for 20 years would require at least $670-704 million, as well as additional unknown costs to address environmental damage. 

Beyond ecological impacts, operation of the Yuma Desalting Plant could jeopardize decades of binational collaboration between the United States and Mexico. The wetland stands as both a vital ecosystem and a symbol of shared stewardship between the United States and Mexico.  Undermining it could erode the diplomatic foundation of the binational Colorado River partnership, complicating future negotiations and diminishing Arizona’s ability to pursue cooperative solutions—such as binational desalination studies—that promise mutual benefit on both sides of the border.

Ultimately, it is not clear that operation of the Yuma Desalting Plant would increase the Central Arizona Water Conservation District’s Colorado River supply. The 1974 Colorado River Basin Salinity Control Act stipulates that “replacement of the reject stream from the desalting plant and of any Wellton-Mohawk drainage water bypassed to the Santa Clara Slough (the bypass flow) […] is recognized as a national obligation.” This provision has ensured that the “bypass flow” has not counted towards Arizona’s use of Colorado River water. If the Yuma Desalting Plant were to operate and the bypass flows reduced, the Central Arizona Water Conservation District may need to reduce its Colorado River diversion by that same amount of water.

Solutions for a Shrinking Colorado River 

Fortunately, there are solutions that we can pursue without sacrificing birds and other wildlife that already struggle in the Colorado River Basin where more than a century of dams and water development eliminated most of the wetlands and riverside forests they need to survive.

The USBR has proposed and implemented projects and programs to increase Colorado River water availability. These include: 1) expansion of water regulating storage in existing reservoirs on the Lower Colorado River to capture flows from local rainstorms and help deliver water more precisely downstream; 2) improved management of salty agricultural return flows in Arizona’s Gila Valley; and 3) system conservation agreements that provide compensation to water users who voluntarily and temporarily conserve water in Lake Mead.  

Under the frameworks of Minutes 323 and 330—the U.S.-Mexico Colorado River collaborative agreements—Mexico is creating benefits for water users in both countries by implementing water efficiency projects in the Mexicali Valley, such as canal lining and installation of automated water control structures, as well as water conservation with programs that provide compensation to water users who voluntarily and temporarily conserve water. The United States and Mexico studied the potential for large ocean desalination facilities that would operate with the best available technology to avoid environmental impacts and could provide new water supplies for Colorado River water users in both countries.

Additionally, the Metropolitan Water District of Southern California, the largest urban supplier relying on Colorado River water, teed up an extensive urban potable reuse project and is inviting urban water suppliers from Arizona and Nevada to share in the project’s costs and benefits.

The challenge of shrinking Colorado River supplies is daunting, but opportunities to meet that challenge without harming the last remaining Colorado River-dependent habitats abound. The Ciénega de Santa Clara is an irreplaceable ecological asset and any decision to operate the Yuma Desalting Plant must account for both ecological protection, economic practicalities, and binational water management objectives. Conservation and reuse generally offer more cost-effective and less risky approaches to water security than operation of the Yuma Desalting Plant. ̽����ѡ hopes the board of the Central Arizona Water Conservation District will reconsider.