Chad, Lake [key], N central Africa. It lies mainly in Chad and Cameroon. Some 550 sq mi (1,425 sq km) in area in 2003, the shallow lake has been greatly reduced in size since the 1960s, when it varied seasonally from c.4,000 to c.10,000 sq mi (10,360–25,900 sq km) and was divided into north and south pools that extended into Nigeria and Niger. At its lowest levels open water was restricted to a portion of the south pool. The reduction in the lake's size was due to a falloff in the monsoons that feed that lake's tributaries and to increased use of water from the tributaries for irrigation. Since then the lake has recovered somewhat, but the north pool, which has suffered from an increase in permanent vegetation and loss of inflow, tends to disappear in the dry season. The Chari River is the chief tributary of Lake Chad, which has no outlets.
Lake Chad was formerly even larger, attaining a depth of c.930 ft (285 m) in the 19th cent.; 60,000 years ago, it covered 150,000 sq mi (388,500 sq km), roughly the size of the Caspian Sea, with most of lake located in what is now central E Chad. The lake also has been much smaller than it was in the mid-20th cent., and probably has previously disappeared: The retreat of the shoreline has revealed sand dunes that were submerged until recently, and the fish found in the lake are adapted to river life.
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