Salton Sea (sôl´tən), saline lake, 370 sq mi (958 sq km), northern part of the Imperial Valley, SE Calif.; 232 ft (71 m) below sea level. Salton Sea was formed as the Colorado River delta grew across the Gulf of California, severing the river's northern part. The area was a salt-covered depression known as Salton Sink until 1905, when a flood on the Colorado broke through an irrigation gap in its levee; 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, its salinity increased, and fertilizer and pesticide pollution grown, harming both fish and bird life as well as the once-thriving tourist trade. A state park and a national wildlife refuge are on its shores; the sea is an important stopping point on the Pacific flyway.