Along the entire coastline of Nigeria lies a belt of mangrove swamp forest from 16 to 96 km (10–60 mi) in width, which is intersected by branches of the Niger and innumerable other smaller rivers and creeks. Beyond the swamp forest is a zone, from 80 to 160 km (50–100 mi) wide, of undulating tropical rain forest. The country then rises to a plateau at a general elevation of about 600 m (2,000 ft) but reaches a maximum of 2,042 m (6,700 ft) on the eastern border in the Shebshi Mountains, and the vegetation changes from woodland to savanna, with thick forest in the mountains. In the extreme north, the country approaches the southern part of the Sahara.
The Niger, the third-largest river of Africa, enters Nigeria from the northwest and runs in a southeasterly direction, meeting its principal tributary, the Benue, at Lokoja, about 550 km (340 mi) from the sea. It then flows south to the delta, through which it empties into the Gulf of Guinea via numerous channels. Other main tributaries of the Niger are the Sokoto and Kaduna rivers. The second great drainage system of Nigeria flows north and east from the central plateau and empties into Lake Chad. Kainji Lake, in the northwest, was created by construction of a dam on the Niger above Jebba.