Mono Lake is a lake in Mono County, California, formed at least 760,000 years ago as a terminal lake in a basin that has no outlet to the ocean. Because it lacks an outlet, dissolved salts make the lake very alkaline and salty. Mono Lake is a desert lake with an unusually productive ecosystem, based on brine shrimp that grow in the lake, and is a critical nesting habitat for two million migratory birds that feed on the shrimp. Mono Lake also notably contains GFAJ-1, a rod-shaped extremophile bacterium that may be capable of incorporating the usually poisonous element arsenic into its biochemistry.
Mono Lake formed from the Mono Basin, an endorheic basin that has no outlet to the ocean. Dissolved salts in the runoff thus remain in the lake and raise the pH levels and salt concentration of the water. The Mono Lake tributaries include Lee Vining Creek and Rush Creek.
Geological forces created the basin over the last five million years. Five million years ago, the Sierra Nevada Mountains were an eroded set of rolling hills and Mono Basin and Owens Valley did not yet exist. The lake is famous for brine shrimp and especially Artemia Monica, a tiny species of brine shrimp, no bigger than a thumbnail and is endemic.
During the warmer summer months, an estimated 4-6 trillion brine shrimp inhabit the lake. Brine shrimp have no food value for humans, but are a staple for birds of the region. The brine shrimp feed on microscopic plank tonic algae, which reproduce rapidly during winter and early spring after winter runoff brings nutrients to the surface layer of water.
The whole food chain of the lake feeds on the high population of single-celled algae present in the warm shallow waters. By March, the lake is as green as pea soup with photosynthesizing algae. Alkali flies, Ephydra hians, live along the shores of the lake and walk underwater encased in small air bubbles to graze and lay eggs. These flies are an important source of food for migratory and nesting birds.