The Salton Sea, a large inland body of water in Southern California, is a unique ecosystem. Once a thriving recreational destination, its changing conditions raise questions about its ability to sustain life. The presence of fish indicates its ecological health, highlighting challenges facing this distinctive desert lake.
Current Fish Populations
Fish exist in the Salton Sea, though their populations are severely diminished. The desert pupfish (Cyprinodon macularius), a federally listed endangered species, is the only fish native to the region, tolerating the sea’s harsh conditions. They survive in salinities from freshwater to twice as salty as seawater, often finding refuge in feeder drains and channels rather than the main body.
Mozambique tilapia (Oreochromis mossambicus), an introduced species, also persists and was once abundant enough for a sport fishery. However, their numbers have drastically declined, too low to sustain fish-eating birds. Other introduced species, like Wami and redbelly tilapia, and western mosquitofish, also persist.
Scientists believe the increasing salinity is nearing a tipping point where even the hardy tilapia may face massive die-offs. Other species that once thrived have largely disappeared from the main body, though some may persist in less saline feeder rivers and canals.
Drivers of Fish Decline
The dramatic reduction in fish populations stems from several interconnected environmental factors, creating an increasingly inhospitable aquatic environment. A primary driver is the escalating salinity of its water. As of November 2024, salinity levels ranged from 68,000 to 86,000 milligrams per liter (mg/L), double that of the Pacific Ocean (35 g/L). The sea is a terminal lake with no natural outflow; as water evaporates, salts accumulate, with approximately 3.6 to 4 million tonnes deposited annually. Salinity has been increasing by roughly 1% annually, making the water too saline for most aquatic life.
Another significant factor is widespread anoxia, or lack of oxygen, particularly in deeper waters. The Salton Sea is a eutrophic system with high nutrient concentrations and frequent low dissolved oxygen levels. When warm surface water mixes with deeper layers, or large algal blooms decay, oxygen is consumed, leading to conditions where fish cannot survive. These deoxygenation events, often occurring from spring to fall, result in massive fish die-offs, predominantly tilapia.
Pollution from agricultural runoff further compounds these problems. It receives agricultural and municipal discharge from the Imperial and Coachella Valleys. This runoff carries dissolved salts, pesticides, and nutrients like phosphorus and nitrogen into the sea. These nutrients contribute to eutrophication and harmful algal blooms, exacerbating oxygen depletion. Additionally, substances like selenium have been detected in Salton Sea fish, though their toxic effects on wildlife have not been observed.
Ecological Implications
The decline of fish populations profoundly affects the Salton Sea’s broader ecosystem, particularly its diverse migratory bird populations. The sea is a crucial stopover on the Pacific Flyway, supporting over 400 bird species, many of which depend on fish. Piscivorous birds like American White Pelicans, Double-crested Cormorants, gulls, and terns historically fed on abundant tilapia. With severe fish reduction, these birds struggle to find sustenance, declining their visits as they seek food elsewhere.
The disruption of the food web extends beyond direct consumption. Fish die-offs contribute to organic material accumulation, further depleting oxygen and fostering diseases. This can lead to massive bird mortality events, such as outbreaks of avian botulism and cholera, transmitted through infected fish or maggots. While some shorebirds may benefit from new food resources as the ecosystem shifts, the loss of a robust fishery threatens the region’s biodiversity and ecological balance. The Salton Sea’s role as a vital wetland for resident and migratory birds is diminished as conditions become less suitable.
Restoration and Management Efforts
Recognizing severe environmental challenges, various initiatives address the Salton Sea’s issues, impacting fish survival. The Salton Sea Management Program (SSMP), led by the California Natural Resources Agency, is a comprehensive effort focusing on habitat restoration, dust suppression, and air quality. A major component is the Species Conservation Habitat (SCH) Project, which began construction in 2021 near the New River.
This project creates over 9,000 acres of ponds and wetlands, providing habitat for fish and birds while reducing dust from exposed lakebed. These habitats use water management strategies to create hospitable conditions. Salton Sea water is blended with less saline river water to control salinity, targeting 20-40 parts per thousand (ppt) for tilapia and other aquatic life.
The federal government committed $250 million through the Inflation Reduction Act, and the state secured over $500 million for these efforts. Other projects include the North Lake Project, restoring 1,600 acres of aquatic habitat, and the Red Hill Bay Restoration Project. The SSMP’s long-term vision also includes evaluating water importation for restoration.