Τhe most famous of the Lakes of Ounianga, a series of Lakes in Borkou-Ennedi-Tibesti Region basin of northeastern Chad. According to the UNESCO description, the lake is in a hot and hyperarid desert. This lake is remnant of a much larger lake which occupied this basin during the African Humid period which lasted from approximately 15,000 to 5,500 years before.
These lakes form a hydrological system that is unique in Earth’s deserts. Ordinarily when water is exposed at the surface in highly arid environments it becomes saline due to a high rate of evaporation. In this case, even though the rate of evaporation from Lake Yoa is equivalent to 5 – 6 meters a year, the total lake depth is 25 meters, unique physical factors combine to keep the lake, fresh.