Formerly Africa's fourth-largest lake, its surface area has been reduced by over 90% since the 1960s due to droughts and diversion of water from such sources as the Chari River. The lake is at the intersection of Chad, Cameroon, Niger, and Nigeria, but most of the remaining water is in Chad and Cameroon. Lake Chad is very shallow and has no outlet, so seasonal rainfall causes large fluctuations in its area.