Salton Sea
Overview
The Salton Sea is-–for now–-topographically separated from the Colorado River, but the two are intimately linked by hydrogeologic history and current tradeoffs in the management of the river’s water resources. By area, the Salton Sea is the largest water body in the contiguous U.S. west of Utah’s Great Salt Lake, covering 305 square miles as of March 2025 [1]. Located in far southeastern California in one of the most arid regions in North America, it is the most recent of a series of large but ephemeral lakes that have formed in this closed basin [2]. The inflows that have maintained the Sea over the last 120 years were significantly curtailed after 2012. The consequent shrinking of the Sea threatens its still-substantial ecological value as well as public health in nearby communities[3][4].
The setting and formation of the Sea
The Sea lies in a depression within a still-active rift valley, the Salton Trough, which is an extension of the Gulf of California [5]. Over the last 6 million years, the Colorado River has carved out enormous canyons along its course and deposited the eroded sediments two miles deep into the Trough, reshaping it into a broad plain stretching 150 miles from present-day Coachella to the Gulf [6]. Prior to the construction of the mainstem dams, the river meandered across this plain, periodically spilling into and then abandoning the depression, creating a water body referred to as Lake Cahuilla [7].
In 1905, the flooding Colorado River breached its banks once again, spilling via the Alamo River and the New River into the then-dry Lake Cahuilla basin, and creating the Salton Sea [8]. The breach was closed in 1907, and since then, the Sea’s existence in the face of extreme aridity has depended on large volumes of incidental agricultural runoff. The runoff originates as Colorado River water applied to more than 500,000 acres of irrigated fields, mainly in the Imperial and Coachella valleys, and in a portion of the Mexicali Valley that drains to the Salton Sea.
The ups and downs of the modern Sea
The cessation of inflows directly from the river in 1907 led to an initial sharp decline in the level of the Salton Sea. The decline was reversed after 1923 by the growth of irrigated agriculture in the Imperial and Coachella valleys and increasing runoff from those fields to the Sea. Over the next 60 years, the Sea gained about 15 feet in elevation [9]. The Sea reached a relatively stable high stand through the 1980s and 1990s, during which total annual inflows were about 1.3 million acre-feet (MAF), 85% of which came from agricultural runoff, less than 10% from municipal and industrial wastewater, and the remainder from precipitation and groundwater [10]. Those inflows were roughly in balance with evaporation from the Sea.
In 2003, water users in California signed the Quantification Settlement Agreement (QSA) to align California’s use of Colorado River water with the Law of the River, in part through the eventual transfer of about 0.4 MAF/year of conserved water from Imperial Irrigation District (IID) and the Coachella Valley Irrigation District to the urban areas of Southern California [11]. These transfers, along with previously established transfers from IID, decreased New River and Alamo River flow from Mexico, and increased consumptive use by emergent wetlands growing atop exposed lakebed, have reduced total inflows to the sea to less than 1.0 MAF annually, a decrease of 30% since 2000 [12]. The System Conservation Implementation Agreement (SCIA) signed by IID and Reclamation in 2024 makes possible further reductions in IID’s water use, up to 0.3 MAF/yr, through 2026, in order to maintain upstream storage in Lake Mead [13]. The Salton Sea physically manifests the tradeoffs inherent in these agreements, to the detriment of the keeping water in the Sea.
With sharply reduced inflows since 2003, the Salton Sea’s elevation has fallen by 13 feet and the surface area has shrunk by almost 60 square miles (~16%), reflecting the loss of about 3 MAF of water volume [14]. For decades, the Sea had been gradually becoming more saline as evaporation concentrated the salts and other impurities in the water; since 2000, salinity has jumped by over 80%, to roughly 75 g/L, more than twice the salinity of the oceans. (The unusual water chemistry of the Sea makes it challenging to measure and report salinity values that are consistent with standard benchmarks.) Any additional water conservation efforts that might accompany post-2026 management of the Colorado River would accelerate the rate of lake decline, the rise in salinity, and the amount of lakebed exposed.
The agricultural runoff that sustains the Salton Sea is highly elevated in nutrients such as nitrates and phosphates, feeding extremely high levels of primary productivity. This manifests as periodic harmful algal blooms in the lake and leads to very low levels of dissolved oxygen in the water as algae decays [15].
The Sea as wildlife habitat
Despite the progressive degradation of the Salton Sea, it remains a crucial habitat for wildlife. More than 400 species of resident and migratory birds have been observed at and around the Salton Sea (Figure 2); it is a major stopover on the Pacific Flyway–the major North-South migratory bird route that stretches from Alaska to South America [16]. As over 90% of the wetlands in California along this route have been drained since the 1850s, the Salton Sea has become even more important as wetland habitat for birds [17]. Thirty years ago, the Sea also sustained more than 100 million fish, predominantly tilapia, and with them, tens of thousands of fish-eating birds such as cormorants and pelicans [18].
In the 1990s, huge dieoffs of tilapia from algae-driven botulism coincided with the mass deaths of thousands of Eared Grebes, White Pelicans, and then-endangered Brown Pelicans from outbreaks of infectious avian diseases, and possibly from poisoning by botulism-laden fish [19]. Since then, rising salinity and low oxygen levels have extirpated almost all of the fish in the lake. In the absence of fish, macroinvertebrates, especially the aquatic insects known as water boatmen (Corixidae), currently thrive there, sustaining growing numbers of shorebirds and some duck species [20]. The Salton Sea also provides habitat for two federally listed species: desert pupfish (Cyprinodon macularius) and semi-aquatic bird Yuma Ridgway’s Rail (Rallus obsoletus yumanensis) [21].
Impacts of the shrinking Sea
The concentration of salts and other contaminants in the shrinking Salton Sea also has major implications for the health of people and other species well beyond the Sea’s margins. Each foot of lowered lake level corresponds to thousands of new acres of exposed lakebed, or playa, where those contaminants are exposed and may be entrained in dust emissions. The resulting increase in dust emissions poses additional health threats to the roughly 1.6 million people in the U.S. and Mexico who live in this region, which already fails to meet state and federal air quality standards [22].
To mitigate the human health and ecological impacts of a shrinking Salton Sea, federal, state, and local agencies have spent more than $500 million to date and have committed a similar amount to future projects. More than 5,000 acres of dust suppression projects have been constructed, primarily on the most dust-emissive portions of the playa, and emergent vegetation has grown to cover thousands more acres. The State of California’s Salton Sea Management Program plans to complete and operate almost 2,000 acres of habitat projects in 2025 and an additional 2,800 acres in 2026, towards satisfying a 2028 milestone of 14,900 habitat acres [23].
Data and tools
Salton Sea Management Program (SSMP) Project Tracker
This tool includes different sections to view the progress made under the SSMP Phase 1: 10-Year Plan in one comprehensive location.
Current Information on the Salton Sea
The Pacific Institute reports daily Salton Sea elevations (from the USGS Westmorland gage) and calculates changes in size, volume, and exposed lakebed.
Salton Sea Environmental Timeseries Dashboard
This map-based dashboard displaying water quality and air quality data is maintained by a community science initiative (Salton Sea Environmental Timeseries) that conducts water and air quality monitoring and research on the Salton Sea.
Additional resources
Imperial Irrigation District (IID) - Salton Sea page
This page includes links (in the left column, under “Salton Sea”) to IID's Air Quality Mitigation and Hydrology Monitoring efforts, among others.
IID - Water & QSA Implementation Annual Reports
These annual reports provide more detail on IID's conservation activities and the water transfers.
Audubon - Birds of the Salton Sea
This page provides summary information about avian abundance and diversity and trends, as well as links to periodic reports (bottom of page) detailing the status of birds at the Sea.
Pacific Institute - Salton Sea Zotero library
The Pacific Institute maintains an online library (Zotero database) of journal articles, reports, conference proceedings, book chapters, dissertations and theses, and other publications, across a range of disciplines, related to the Salton Sea.
Salton Sea Summits
These roughly biennial conferences have featured presentations on Salton Sea policy and research. Recordings and copies of these conference presentations are available; see the “Previous Summits” drawdown menu in the upper right corner of the page for additional links.