Lake Chad, lake, central Africa, at the junction of Chad, Cameroon, Nigeria, and Niger, 250 m (820 ft) above sea level. Lake Chad is fed principally by the Chari (Shari) and Logone rivers. Although the lake has no visible outlet, it is steadily decreasing in size because of evaporation and underground seepage. In the rainy season the area of the lake is as great as 25,900 sq km (10,000 sq mi), but in the dry season it shrinks to as little as 10,000 sq km (4000 sq mi). In open water the depth of the lake varies from 1 m (3 ft) in the northwest to 6 m (20 ft) in the south. The numerous islands lying along the eastern shore of the lake are inhabited. The first Europeans to visit the lake were a party of British explorers in 1823.