Some of the prefectures are named for the major rivers of the area. The Mayo Kébi River drains into the Bénoué, and thus finally to the Gulf of Guinea. The Chari, and its tributaries, including the Logone (with two branches, Logone Occidental and Logone Oriental) and Bahr Salamat, flow into Lake Chad. The Batha is an intermittent river, ending at Lake Fitri. Lakes Chad and Fitri grow and shrink according to the amount of rainfall. Bas (Lower) means downstream. Moyen means middle. Chari is a local word meaning river.