Lake Turkana, formerly known as Lake Rudolf, is a lake in the Kenyan Rift Valley, in northern Kenya, with its far northern end crossing into Ethiopia. It is the world's largest permanent desert lake and the world's largest alkaline lake. By volume it is the world's fourth-largest salt lake after the Caspian Sea, Issyk-Kul, and Lake Van, and among all lakes it ranks 24th.
Lake Turkana is now threatened by the construction of Gilgel Gibe III Dam in Ethiopia due to the damming of the Omo river which supplies most of the lake's water.
Although the lake commonly has been —and to some degree still is— used for drinking water, its salinity and very high levels of fluoride generally make it unsuitable, and it has also been a source of diseases spread by contaminated water. Increasingly, communities on the lake's shores rely on underground springs for drinking water. The same characteristics that make it unsuitable for drinking limits its use in irrigation. The climate is hot and very dry.
The rocks of the surrounding area are predominantly volcanic. Central Island is an active volcano, emitting vapour.