Lake Chad is a shallow fresh water lake (only about 10 m at its deepest) at the border of Chad, Nigeria, Niger, and Cameroon. The lake is a remnant of a former inland sea. Since the 1960s, the lake has shrunk from its original area of 26,000 km² to about 1,500 km² in 2000. Overgrazing, increased human water use, and shifting climate patterns are considered as being the cause of the decrease in extent. Less than half of the lake's area is water-covered throughout the entire year, with the remaining area consisting of wetlands.