The Chad Basin is the largest endorheic drainage basin in Africa, centered on Lake Chad. It has no outlet to the sea and contains large areas of desert or semi-arid savanna. The drainage basin is roughly coterminous with the sedimentary basin of the same name, but extends further to the northeast and east. The basin spans seven countries, including most of Chad and a large part of Niger. It has an ethnically diverse population of about 30 million people as of 2011, growing rapidly. A combination of dams, increased irrigation, and reduced rainfall are causing shortages of water. Lake Chad continues to shrink.