Over millions of years, the Colorado River
has flowed into the Imperial Valley and deposited soil (creating fertile farmland) and building up the terrain, constantly changing the course of the river. For the next thousands of years, the river has flowed into and out of the valley alternately, creating a freshwater lake, an increasingly saline lake, and a dry desert basin, depending on river flows and the balance between inflow and evaporative loss. The cycle of filling has been about every 400–500 years and has repeated itself many times. The latest natural cycle occurred around 1600–1700 as remembered by Native Americans who talked with the first settlers. Fish traps still exist at many locations, and the Native Americans evidently moved the traps depending upon the cycle.
The most recent inflow of water from the now heavily controlled Colorado River was accidentally created by the engineers of the California Development Company
in 1905. In an effort to increase water flow into the area for farming, irrigation canals were dug from the Colorado River into the valley. Due to fears of silt buildup, a cut was made in the bank of the Colorado River to further increase the water flow. The resulting outflow overwhelmed the engineered canal, and the river flowed into the Salton Basin for two years, filling the historic dry lake bed and creating the modern sea, before repairs were completed.
While it varies in dimensions and area with fluctuations in agricultural runoff and rainfall, the Salton Sea is about 15 miles (24 km) by 35 miles (56 km). With an estimated surface area of 343 square miles (890 km2) or 350 square miles (910 km2), the Salton Sea is the largest lake in California
The average annual inflow is less than 1,200,000 acre feet
(1.5 km3), which is enough to maintain a maximum depth of 44 feet (13 m) and a total volume of about 6,000,000 acre feet
(7.4 km3). However, due to changes in water apportionments agreed upon for the Colorado River under the Quantification Settlement Agreement
of 2003, the overall water level of the sea is expected to decrease significantly between 2013 and 2021