Mono Lake in eastern California is an ancient saline soda lake in the closed Mono Basin, where evaporation leaves minerals behind and creates highly alkaline water. Shaped by long geologic activity, it occupies the remnant of prehistoric Lake Russell and remains surrounded by volcanic features, including Panum Crater and Paoha Island. Its famous tufa towers formed underwater where spring water met lake water, then were exposed as lake levels fell. Though fishless, the lake supports brine shrimp, alkali flies, and about two million migratory waterbirds annually. In the 20th century, stream diversions to Los Angeles sharply lowered the lake until legal action helped secure its partial recovery.