Mono Lake is an alkaline lake just east of Yosemite and the Sierra Nevada. It is best known for the tufa spires around its shore. These were formed underwater by lake bottom springs and became exposed when the lake level dropped. The lake level dropped after the City of Los Angeles diverted the streams that feed the lake for its water supply. Lake levels are rising again after LA was forced to allow some of the stream waters flow again into the lake. Mono Lake is a very important area for migrating birds which feed on its teeming brine shrimp and alkali flies. These same alkali flies were once collected as food by the native American tribe that once lived here. There are no fish in Mono Lake.