The Salton Sea, located in the vast, arid desert of Southern California, is the state’s largest inland lake, stretching across parts of Imperial and Riverside counties. This massive body of water, which sits well below sea level, is not a natural feature but was formed largely by accident in the early 20th century. Between 1905 and 1907, an engineering failure caused the Colorado River to breach an irrigation canal, flooding the Salton Sink for nearly two years before the flow was finally stopped. The lake that remained has since become a dying, toxic terminal body of water, facing an environmental crisis driven by a combination of human activity and unforgiving desert geography.
The Origin of the Crisis: Agricultural Input
The modern Salton Sea is sustained almost entirely by an inflow of agricultural runoff from the surrounding Imperial and Coachella Valleys. Water from the Colorado River is diverted to these areas for irrigation, and the excess water, known as tailwater, drains into the lake via the New and Alamo Rivers. This inflow from the Imperial Valley, one of the most productive agricultural regions in the United States, carries the chemical burden of intensive farming practices.
This runoff is saturated with the remnants of fertilizers, leading to a significant influx of nutrients such as nitrogen and phosphorus. These nutrients fuel excessive growth of algae, a process called eutrophication. Along with nutrients, the agricultural flow carries pesticides and herbicides, including organophosphorus insecticides like chlorpyrifos and diazinon, which have been detected in the sea’s main tributaries.
The Mechanism of Toxicity: Salinity and Concentration
The toxicity of the Salton Sea is exponentially magnified because it is an endorheic basin, meaning it has no natural outflow to the ocean. In the desert’s extreme heat, the water that flows into the lake leaves only through rapid evaporation, which occurs at a rate of approximately 5.5 feet of surface water annually. This physical process concentrates everything that the agricultural runoff brings in, including salts and chemical contaminants.
The result is a hyper-saline environment where the concentration of dissolved solids far exceeds that of the Pacific Ocean. The salinity of the Salton Sea has reached levels over 50% greater than ocean water, making the aquatic environment increasingly inhospitable to life. The excessive nutrient loading triggers massive algal blooms, and when these organisms die and decompose, they consume vast amounts of dissolved oxygen. This creates anoxic conditions, or “dead zones,” in the deeper parts of the lake, particularly during the hot summer months. This lack of oxygen exacerbates the toxicity, leads to the release of noxious gases like hydrogen sulfide, and can mobilize toxic metals from the lake bottom.
Hazardous Byproducts: Exposed Playa and Toxic Dust
As the water level declines, vast stretches of the former lakebed, known as the playa, are exposed to the air. This exposed playa is not benign sand but a layer of dried, fine sediment that has accumulated decades of concentrated agricultural waste and toxic elements. The sediment composition includes heavy metals such as arsenic, cadmium, copper, and zinc, which are present at levels of ecological concern.
A particularly hazardous element found in the sediment is selenium, which originates from the Colorado River water and is concentrated by agricultural practices. When high winds sweep across the exposed playa, they loft this fine, contaminated sediment into the atmosphere, creating a severe regional public health hazard. This toxic dust consists of small particulate matter which is small enough to be inhaled deep into the lungs. This airborne contamination is contributing to disproportionately high rates of respiratory illnesses, including asthma, in the surrounding communities, with some local areas reporting childhood asthma rates three times the national average.
Immediate Environmental Consequences
The extreme toxicity and hyper-salinity of the Salton Sea have caused a collapse of the aquatic food chain. The increasing salt concentration has eliminated nearly all fish species, leaving only the hardy tilapia as the last remaining species. However, even the resilient tilapia struggle to survive the escalating salinity and frequent anoxic events, leading to massive fish die-offs that litter the shoreline.
This ecological failure has a devastating effect on the millions of migratory birds that use the Salton Sea as a major stopover point on the Pacific Flyway. The loss of the fish population, which served as a primary food source, severely compromises the habitat for fish-eating birds like pelicans and cormorants. The shrinking habitat also forces birds to crowd into smaller areas, which increases the risk of disease outbreaks, such as avian cholera, leading to mass bird mortality events.