The Salton Sea sits in a deep geological depression in Southern California, known as the Salton Trough or Salton Sink. While this desert location has a long history of intermittent flooding, the modern sea, California’s largest lake, is a direct and unintended consequence of human engineering and failure. Its existence, size, and ecological state are entirely dependent on water management decisions and agricultural practices. This unique inland body of water is a relatively new geographical feature, born from a catastrophic man-made flood in the early 20th century.
The Ancient History of Water in the Basin
The Salton Sink, situated below sea level, is a geographical feature that has periodically held vast amounts of water over millennia. This low-lying area was repeatedly filled and dried out by the shifting course of the Colorado River. The most notable of these natural water bodies was Lake Cahuilla, which was massive compared to the present Salton Sea. At its peak, Lake Cahuilla was approximately six times larger and over 300 feet deep, extending north past the modern city of Indio.
The Colorado River would occasionally shift its delta, diverting its flow northward into the basin, creating a large, freshwater lake. When the river shifted back toward the Gulf of California, the lake would be abandoned to the desert heat. With no natural outflow, the water in Lake Cahuilla would slowly disappear through evaporation, leaving behind a dry, salt-encrusted lakebed. This cycle occurred multiple times over thousands of years, with the last major infilling event happening around the late 1500s. This history confirms the basin was naturally susceptible to becoming a large lake.
The 1905 Engineering Failure
The modern Salton Sea was created directly by the efforts of the California Development Company (CDC) to bring water to the Imperial Valley for agriculture. Beginning in 1901, the CDC constructed the Imperial Canal system to divert water from the Colorado River. The initial control gates proved inadequate to handle the river’s heavy sediment load, which quickly clogged the main channel and threatened the water supply to the farms.
To solve the silt problem, engineers created an unprotected cut in the riverbank several miles south in Mexico, allowing the river to flow directly into the irrigation canal. This temporary solution lacked proper control structures. When heavy rainfall and snowmelt caused the Colorado River to swell in early 1905, the floodwaters surged through this breach. The entire volume of the Colorado River was soon diverted away from the Gulf of California and channeled into the Salton Sink.
The resulting uncontrolled flood poured into the basin through the New and Alamo riverbeds. For nearly two years, from 1905 until February 1907, engineers struggled to contain the full force of the river flowing into the deep depression. It took a concerted effort by the Southern Pacific Railroad, dumping trainloads of rock and earth, to finally close the breach and redirect the river back to its original channel. This catastrophic two-year inundation created the Salton Sea, covering an area of approximately 400 square miles.
The Geography of Retention
The Salton Sea’s continued existence for over a century is explained by the region’s geography and ongoing human activity. The Salton Sink is an endorheic basin, meaning it is a closed system with no outlet to the ocean. Any water that flows into the basin can only leave through evaporation.
The sea is not sustained by natural rainfall, which is scarce in the Sonoran Desert, but by a continuous, artificial source of inflow. The vast majority of the water comes from agricultural runoff from the surrounding Imperial and Coachella valleys. This runoff, delivered by the Alamo and New Rivers, is essentially excess irrigation water that gravity carries into the lowest point of the valley. This constant, regulated inflow has prevented the modern sea from fully evaporating, unlike Lake Cahuilla.
Current Environmental Crisis and Consequences
The sea’s closed nature and reliance on agricultural runoff have created a severe environmental and public health crisis. Since it has no outlet, evaporation leaves behind all dissolved salts and minerals, causing the sea to become hypersaline. The current salinity is nearly double that of the Pacific Ocean, making the water uninhabitable for most fish species and leading to massive fish and bird die-offs.
The agricultural runoff also carries a toxic cocktail of contaminants, including pesticides, selenium, and high concentrations of nitrogen and phosphorus. As water levels have dropped, vast stretches of the former lakebed, known as the playa, have become exposed. When the wind sweeps across this exposed playa, it kicks up clouds of fine, toxic dust laced with these pollutants and heavy metals. This dust poses a serious public health risk, contributing to some of the nation’s worst air quality and resulting in elevated rates of asthma and other respiratory illnesses in nearby communities.