Lake Rudolf, which is also known as Lake Turkana, lies in the eastern arm of the great Rift Valley. It is primarily fed by the Omo River, which flows south from the Ethiopian highlands and sits in an inhospitable landscape of dormant volcanoes, wind-driven semidesert, and old lava flows. During the morning hours, strong gusts of wind usually blow from the east down the slopes of Mount Kulal and across the surface of the lake. This unrelenting wind creates large, white-capped waves on the lake's surface and makes navigation almost impossible. It also gives the lake a bluish color, reflecting the clear sky above. However, when the wind dies down in the afternoon, the lake takes on the color of green jade, due to algae that rise to the surface when the waters are calm. It is because of this afternoon and evening color that the lake has long been known as the Jade Sea (Imperato: 1998:3).