The Athi-Galana-Sabaki River is the second longest river in Kenya (after the Tana River). It has a total length of 390 km and drains an area of 70 000 km². The Athi River is called the Galana and Sabaki in its lower course. The upper Athi River drains the eastern slopes of the Aberdare Ranges north of Nairobi just, south of the Equator; the Tsavo River, its main tributary, drains the Kenyan slopes of Mt. Kilimanjaro. It is joined by the Nairobi River along its course.