Lake Yoa is the most famous, and second largest of a series of Lakes in Borkou-Ennedi-Tibesti Region basin of northeastern Chad. It is locaded in the Ounianga Kebir about 40km west of Ounianga Sarir. These lakes are remnants 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 present. There are currently 15 lakes in the basin with a total surface area of approximately 20 kilometres (12 mi) square.