Turkana, Lake, c.2,500 sq mi (6,475 sq km), NW Kenya and SW Ethiopia, E Africa, in the Great Rift Valley; alt. 1,230 ft (375 m). Surrounded by desolate, volcanic mountains, the 170-mi-long (274-km) alkaline lake is the focus of interior drainage and has no outlet; it is becoming increasingly saline. The Omo River, in Ethiopia, supplies most of the lake's water; development of the river for hydropower and irrigation has reduced inflow. Fishing and tourism are economically important. Nearby is Kanapoi, an archaeological site with 4.1-million-year-old australopithecine fossils. It was formerly known as Lake Rudolf.