Lake on the northeastern boundary of Nigeria and the eastern boundary of Chad. It lies in a basin of inland drainage and once varied in extent between rainy and dry seasons from 50,000 sq km/19,000 sq mi to 20,000 sq km/7,000 sq mi, but a series of droughts (and loss of water through evaporation and seepage underground) between 1979 and 1989 reduced its area to 2,500 sq km/965 sq mi by 1993; the loss of area is continuing. It is a shallow lake (depth does not exceed 5–8 m/16–26 ft), with the northern part being completely dry and the southern area being densely vegetated, with swamps and open pools. The lake was first seen by European explorers in 1823.
The south Chad irrigation project used the lake waters to irrigate the surrounding desert, but the 4,000 km/2,500 mi of canals dug for the project are now permanently dry because of the shrinking size of the lake. The Lake Chad basin is being jointly developed for oil and natron (sodium carbonate, used in the manufacture of soap and medicines) by Cameroon, Chad, Niger, and Nigeria.
The lake is situated at the junction of the boundaries of Nigeria, Cameroon, Niger, and Chad and is all that remains of a former inland sea. It is fed principally by the River Chari from the south, and has no outlet. Its shore is marshy, and the lake itself contains many islands. The salinity increases steadily from south to north. The diminishing area of the lake has ruined the livelihood of the local fishing community.