Salton Sea [key], saline lake, 370 sq mi (958 sq km), northern part of the Imperial Valley, SE Calif.; 232 ft (71 m) below sea level. The area was anciently the northern part of the Gulf of California, but during the Pleistocene the Colorado River delta grew across the gulf, severing the Imperial Valley from the gulf. Subsequently, during periods of plentiful rainfall, a lake formed in the region, but when the Spaniards arrived (c.1600) the area was a salt-covered depression that became known as Salton Sink. In 1905 a flood on the Colorado overwhelmed an irrigation canal and broke its levees; the river flowed into the sink for two years before being checked. The water level rose due to runoff from surrounding mountains and irrigation systems, but in recent years the sea's size has decreased due to drought, improvements in irrigation that reduced excess water for runoff, and the transfer of water away from the Imperial Valley to urban areas. As a result, salinity has increased, and fertilizer and pesticide pollution has grown, harming both fish and bird life as well as the once-thriving tourist trade. Airborne dust from the now-exposed dry lakebed also is a health hazard. A state park and a national wildlife refuge are on its shores. The sea has been an important stopping point on the Pacific flyway, but increased salinity and pollution threatens to make the sea inhospitable.
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