Lake Chad is a historically large, shallow, endorheic

Endorheic

An endorheic basin is a closed drainage basin that retains water and allows no outflow to other bodies of water such as rivers or oceans...

 lake

Lake

A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...

 in Africa

Africa

Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

, whose size has varied over the centuries. According to the Global Resource Information Database of the United Nations

United Nations

The United Nations is an international organization whose stated aims are facilitating cooperation in international law, international security, economic development, social progress, human rights, and achievement of world peace...

 Environment Programme, it shrank as much as 95% from about 1963 to 1998; yet it also states that "the 2007 (satellite) image shows significant improvement over previous years". Lake Chad is economically important, providing water

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 to more than 20 million people living in the four countries that surround it (Chad

Chad

Chad , officially known as the Republic of Chad, is a landlocked country in Central Africa. It is bordered by Libya to the north, Sudan to the east, the Central African Republic to the south, Cameroon and Nigeria to the southwest, and Niger to the west...

, Cameroon

Cameroon

Cameroon, officially the Republic of Cameroon , is a country in west Central Africa. It is bordered by Nigeria to the west; Chad to the northeast; the Central African Republic to the east; and Equatorial Guinea, Gabon, and the Republic of the Congo to the south. Cameroon's coastline lies on the...

, Niger

Niger

Niger , officially named the Republic of Niger, is a landlocked country in Western Africa, named after the Niger River. It borders Nigeria and Benin to the south, Burkina Faso and Mali to the west, Algeria and Libya to the north and Chad to the east...

, and Nigeria

Nigeria

Nigeria , officially the Federal Republic of Nigeria, is a federal constitutional republic comprising 36 states and its Federal Capital Territory, Abuja. The country is located in West Africa and shares land borders with the Republic of Benin in the west, Chad and Cameroon in the east, and Niger in...

) on the edge of the Sahara Desert.