Background Information on the Salton Sea

The Salton Sea, located in southern Riverside and northern Imperial counties in Southern California, is California' s largest lake (map at right). Although large seas have cyclically formed and dried over historic time in the basin due to natural flooding from the Colorado River, the current Salton Sea was formed when Colorado River floodwater breached an irrigation canal being constructed in the Imperial Valley in 1905 and flowed into the Salton Sink. The Sea has since been maintained by irrigation runoff in the Imperial and Coachella valleys and local rivers. Because the Sea is a terminal lake, increasingly concentrated salts have resulted in a salinity that is currently 50 percent greater than that of the ocean. The increasing salinity and other water quality issues, including temperature extremes, eutrophication, and related anoxia and algal productivity, are adversely influencing the Sea' s fish and wildlife resources.

Large scale map of Salton Sea
Map Overview of Salton Sea. (Open PDF in new tab)
Agricultural Fields irrigated from Colorado River and providing runoff to Salton Sea
Agricultural Fields irrigated from Colorado River.

The Salton Sea functions both as a sump for agricultural runoff (photo right) and an important wildlife area r from the Colorado River (Imperial Irrigation District [IID] 2010), while about 50,000 acres are farmed in the Coachella Valley (County of Riverside, Agricultural Commissioner' s Office 2010).

Although it has only existed for about 100 years, the Salton Sea has become an extremely critical resource for many species of resident and migratory birds, including several species of special concern. Due to the significant loss of wetlands in California and other areas, the Salton Sea ecosystem has become one of the most important wetlands for birds in North America and supports some of the highest levels of avian biodiversity in the southwestern United States. Recent studies have documented the great importance of the Salton Sea ecosystem in providing habitat for migrating and resident waterbirds, particularly Pacific Flyway waterbirds. More than 400 resident, migratory, and special status bird species have been recorded in the Salton Sea area since its formation, with about 270 of those species using the Salton Sea on a fairly regular basis. In addition to the diversity of birds, studies have indicated that the large number of individual birds using the Salton Sea is even more ecologically relevant than the number of species.

Until recently, the Sea also supported a robust marine sport fishery that included orangemouth corvina (Cynoscion xanthulus), Gulf croaker (Bairdiella icistia), and sargo (Anisotremus davidsoni). Increasing salinity has eliminated the marine fishery, leaving only the euryhaline tilapia to provide sport fishing. Tilapia and several smaller nonsport fish species, of which only the endangered desert pupfish (Cyprinodon macularius) is native, currently sustain a number of bird species.

Declining inflows in future years will result in collapse of the Salton Sea ecosystem due to increasing salinity and other water quality issues, such as temperature, eutrophication, and related anoxia and algal productivity. Pileworms and barnacles, primary components of the Salton Sea food web, already appear to be impacted by deteriorating water quality. Tilapia, which is presently the primary forage species for piscivorous (fish-eating) birds at the Salton Sea, may be eliminated when salinity exceeds 60 parts per thousand (ppt). Salinity reached 50 ppt in 2008 and could exceed 60 ppt as early as 2018. Tilapia would likely continue to persist in areas of lower salinity where the rivers, creeks, and agricultural drains enter the Salton Sea. However, the loss of fish populations from the open water area would significantly reduce and possibly eliminate use of the Salton Sea by piscivorous birds, such as pelicans, double-crested cormorants, and black skimmers by the early 2020s. Some of these birds could use the areas where the rivers, creeks, and drains enter the Salton Sea if fish continue to persist in these locations. In addition, the relative abundance of bird species that forage on invertebrates likely would change over time with increases in salinity and resultant changes in the invertebrate community.

The Quantification Settlement Agreement (QSA) is one of the factors contributing to declining inflows to the Salton Sea. California historically used more than its normal year apportionment of Colorado River water, obtaining the excess from water apportioned to Arizona and Nevada but not used by those states, and by water designated as surplus by the Secretary of the Interior. The amount of unused apportionment previously available to California has diminished, however, and is unlikely to be available in the future. After prolonged negotiations between the Federal government and the California water districts that have entitlements to Colorado River water, a series of agreements, collectively known as the QSA, were made among the Federal government, State of California, IID, Metropolitan Water District of Southern California , San Diego County Water Authority, and Coachella Valley Water District in October 2003. The QSA imposes water conservation measures within the IID service area to allow the transfer of this water elsewhere, which reduces the volume of agricultural runoff that constitutes the Salton Sea's chief source of water. IID is required to provide conserved water to the Sea to mitigate the effects of the transfer on salinity until 2017. After 2017, however, the Sea's salinity is expected to exceed the tolerance limit for fish and, thus, mitigation for effects on salinity ceases at that time. The reduction in water to the Sea after 2017 is anticipated to result in loss of the fishery, exposure of soils to wind erosion, and bird declines due to loss of food. Reduction of inflows to the Sea from other factors, such as water recycling in Mexico, is also contributing to increases in salinity and a declining sea elevation. IID is currently petitioning to provide conserved water to the Salton Sea until 2014 rather than 2017 so that funds be employed for habitat mitigation sooner. The Imperial Irrigation District is currently in the process of preparing a Natural Community Conservation Plan (NCCP) and Habitat Conservation Plan (HCP) in consultation with CDFW and the United Sates Fish and Wildlife Service (USFWS). For more information, visit the IID website.


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