Lake Chad is the large lake at the southern edge of the Sahara that has repeatedly expanded and shrunk as rainfall changed.
It lies where Chad, Cameroon, Nigeria, and Niger meet, in the Sahel transition zone south of the central Sahara. Lake Chad is a shallow freshwater lake whose open water, wetlands, and islands vary greatly with seasonal rains and inflow from the Chari and Logone rivers.
During the African Humid Period, the lake expanded dramatically and formed part of a much larger ancient water system. In the late twentieth century, reduced rainfall combined with growing irrigation demand caused a major contraction, making Lake Chad a prominent example in discussions of desertification and water security.
The lake has not simply disappeared: its size fluctuates, and its wetlands remain important for fishing, farming, grazing, and wildlife. Maps may differ because some measure open water while others include surrounding marshes and seasonally flooded areas.