Lake, western Africa.
Located at the juncture of the boundaries of Nigeria, Niger, and Chad, its southern part forms the northern extent of Cameroon. Fed by the Chari River , its area varies from year to year, usually ranging between 3,800 and 9,900 sq mi (9,850 and 25,600 sq km). Its water level has been dropping since the 1970s, a change apparently related to the desertification of the surrounding Sahel region. The lake was first explored by Europeans in 1823.