Lake Chad is a historically large, shallow, endorheic lake in Central Africa, which has varied in size over the centuries. According to the Global Resource Information Database of the United Nations Environment Programme, it shrank by as much as 95% from about 1963 to 1998. The lowest area was in 1986, at 279 km², but "the 2007 image shows significant improvement over previous years." Lake Chad is economically important, providing water to more than 30 million people living in the four countries surrounding it on the central part of the Sahel. It is the largest lake in the Chad Basin.