The Salton Sea, California’s largest inland lake, is a unique body of water located in the Sonoran Desert across Southern California’s Riverside and Imperial counties. This terminal lake, meaning it has no natural outflow other than evaporation, sits significantly below sea level, roughly 200 to 237 feet. The modern Salton Sea formed unexpectedly in 1905 when Colorado River water breached an irrigation canal, flowing continuously into the basin for two years. Since its formation, the lake has been sustained primarily by agricultural runoff from the surrounding Imperial and Coachella Valleys.
The Salton Sea’s Original Aquatic Life
Before the accidental formation of the modern Salton Sea, the basin experienced cyclical filling and drying over millennia, creating ancient lakes like Lake Cahuilla, fed by the Colorado River. Archaeological evidence from sites around the Salton Basin and the lower Colorado River indicates the presence of several native fish species. These included the Bonytail (Gila elegans), Razorback Sucker (Xyrauchen texanus), Colorado Pikeminnow (Ptychocheilus lucius), Striped Mullet (Mugil cephalus), and Machete (Elops affinis).
Bonytail and Razorback Sucker remains comprised nearly 99% of the fish found in Lake Cahuilla sites, indicating their dominance in this fluctuating freshwater or brackish environment. These native species were adapted to the dynamic conditions of the Colorado River and its ancient flood-formed lakes. However, as the Salton Sea’s salinity increased after its 1905 formation, these freshwater fish populations gradually disappeared.
Introduced Species and Their Adaptation
After the Salton Sea’s formation, initial fish populations included freshwater species that arrived with the Colorado River’s inflow. A commercial fishery for Striped Mullet operated from 1915 to 1953, peaking at 91,000 pounds in 1918. Mullet entered via the Colorado River and Alamo Canal, but their access was cut off after 1942 when the All American Canal replaced their migration route.
From 1929 to 1956, the California Department of Fish and Game undertook extensive efforts, introducing over 30 different marine species to foster a sport fishery in the evolving saline environment. These species were largely sourced from the Gulf of California, particularly near San Felipe. Among the most successful introductions were the Orangemouth Corvina (Cynoscion xanthulus), Bairdiella (Bairdiella icistia), and Sargo (Anisotremus davidsoni), which established thriving populations.
Tilapia, specifically a hybrid form of Mozambique Tilapia (Oreochromis mossambicus), were not intentionally introduced for sport fishing. They escaped into the Salton Sea in the 1960s from tropical fish farms or irrigation canals where they were used for algae control. These introduced species adapted well to the Salton Sea’s challenging conditions, including high salinity and warm temperatures. Mozambique Tilapia, for instance, can tolerate salinities up to 120 parts per thousand (ppt) and reproduce at 69 ppt, thriving in temperatures between 25-30°C.
Orangemouth Corvina, Bairdiella, and Sargo also tolerated salinities reaching 50-57.5 ppt in laboratory tests, allowing them to flourish. The Corvina, a prized game fish, exhibited rapid growth, contributing to the sea’s recreational appeal. The Salton Sea’s fishery, supported by these introduced species, peaked in the 1960s, becoming a popular destination for anglers.
Current Fish Populations and Challenges
The Salton Sea’s fish populations have declined due to escalating salinity, frequent anoxia events, and pollution. The sea’s salinity is now approximately 50% greater than ocean water, at around 44,000 milligrams per liter (44 ppt), and steadily increases by about 1% annually. This rising salinity, particularly exceeding 45 ppt, hinders the spawning success of many fish species, including the once-abundant Corvina.
Anoxia, or low dissolved oxygen levels, frequently occurs due to massive algal blooms fueled by nutrient-rich agricultural runoff. These blooms consume oxygen when they decompose, leading to widespread fish die-offs. Temperature fluctuations and pollution from pesticides and heavy metals further degrade water quality and stress aquatic life.
By 2003, the Orangemouth Corvina had largely disappeared. Currently, the only fish species persisting in significant numbers are Tilapia and the endangered Desert Pupfish. However, even Tilapia populations are dwindling, succumbing to extreme salinity, low oxygen, and parasitic infestations. Salinity is approaching a threshold for their survival.
The Desert Pupfish, known for its high tolerance to saline conditions, primarily inhabits the fresher waters of riparian zones and wetlands surrounding the sea. Their populations are also declining, and increasing salinity threatens to impede their movements between these habitats. The reduction in fish populations has led to a decrease in fish-eating bird species that once frequented the Salton Sea.