Salton Sea Transboundary Watershed

Salton Sea Watershed Staff Report (click here for the staff report)

The Salton Sea Transboundary Watershed (USGS Hydrologic Unit 18100200) is the Priority Watershed in the Colorado River Basin Region. It encompasses one-third of the region (about 8,360 square miles) and contains five (out of a total of six) of the Region's impaired surface waterbodies. Most of the watershed is in Imperial County. The watershed has been identified as a Category I (impaired) Watershed under the 1998 California Unified Watershed Assessment (UWA). The California UWA was developed and implemented in response to the Clean Water Action Plan released by President William Clinton and Vice-President Albert Gore on February 19, 1998. The UWA was a collaborative process between the State and the United States Environmental Protection Agency (USEPA) and was developed to guide allocation of new federal resources for watershed protection.



The watershed contains five main surface waterbodies: the Salton Sea, the New River, the Alamo River, the Imperial Valley Agricultural Drains, and the Coachella Valley Stormwater Channel.

The Salton Sea is California's largest lake and was famous for its sport fishery and recreational uses. It is about 35 miles long and 9-15 miles wide with approximately 360 square miles of water surface and 105 miles of shoreline. The surface of the sea lies approximately 232 feet below sea level. One of the major functions of the Salton Sea is to serve as a sump for agricultural wastewater for the Imperial and Coachella Valleys. Executive Order of Withdrawal (Public Water Reserve No. 114, California No. 26), signed in 1928, designated lands within the Salton Basin below elevation 220 feet below MSL as storage for wastes and seepage from irrigated lands in the Imperial Valley. Approximately 75% of the freshwater inflow to the Sea is agricultural drain water from Imperial Valley. As the Sea has no outlets, salts concentrate in it and nutrients enhance the formation of eutrophic conditions. Currently, the Sea is 25% saltier than the ocean, with salinity increasing at approximately 1% per year. The Sea supports a National Wildlife Refuge and is a critical stop on the Pacific Flyway for migrating birds, including several state- and federal-listed endangered and threatened species. The Salton Sea National Wildlife Refuge was established in 1930 to preserve wintering habitat for waterfowl and other migratory birds. However, catastrophic die-off of birds and fish between 1992 and 1997 indicate the Sea is in serious trouble, and may be unable to support these beneficial uses in the future.

The New River originates in Mexico. It flows approximately 20 miles through the City of Mexicali, Mexico, crosses the International Boundary, continues through the City of Calexico in the United States, and travels northward about 60 miles until it empties into the Salton Sea. Its flow at the International Boundary is about 150 to 200 cubic feet per second (cfs). (108,400 to 145,000 acre-feet per year (AFY)). The New River carries urban runoff, untreated and partially treated municipal wastes, untreated and partially treated industrial wastes, and agricultural runoff from the Mexicali Valley, Mexico across the International Boundary into the United States. In addition, the River carries urban runoff, agricultural runoff, treated industrial wastes, and treated, disinfected and non-disinfected domestic wastes from the Imperial Valley. It also carries approximately 6 to 11 cfs (4,350 to 7,970 AFY) of treated wastewater from point sources in Imperial Valley. The New River flow at the Salton Sea is about 600 cfs (430,000 AFY).

The Alamo River originates approximately 2 miles south of the International Boundary with Mexico, and flows northward across the border for about 50 miles until it empties into the Salton Sea. The Alamo River is dominated by agricultural return flows from Imperial Valley. It also carries approximately 15 to 27 cfs (10,867 to 19,200 AFY) of treated wastewater from point sources in Imperial Valley. Its flow at the International Boundary is 3 to 5 cfs (2100 to 3620 AFY), whereas at its delta with the Salton Sea is about 800 to 1000 cfs (600,000 to 800,000 AFY).

The Ag Drain system comprises over 1,450 miles of surface drains, which discharge into the Alamo and New Rivers and the Salton Sea [2.11]. The Ag Drains primarily carry agricultural runoff from the Imperial Valley. Agricultural discharges in the Imperial Valley average about 830,000 acre-feet/year. Of this amount, approximately 36 percent is tailwater, 33 percent is seepage, and 30 percent is tilewater. The resulting mix of tailwater, tilewater, and seepage contains pesticides, nutrients, selenium, and silt in amounts that violate water quality standards.

For more information:

  • We have compiled a comprehensive list of links of agency, academia, and NGO websites focused on the Salton Sea watershed.

  • California Rivers Assessment: This site is developed and maintained by the Univeristy of California, Davis Information Center for the Environment (ICE). To find out more about the Salton Sea Watershed, select "Search by Basin", then use the pull down menu on the top and selct "Salton Sea".