The Mare aux Hippopotames (Lake of Hippopotamuses) is a lake and national park in Burkina Faso, created in 1937 and designated in 1977 as the only UNESCO Biosphere Reserve in the nation. The park was created around a freshwater lake and includes surrounding pools and marches in the flood plain of the Black Volta River, and surrounding forests. The park is home to about 100 hippos; about 1000 eco-tourists visit each year. It is located about 60 kilometers (37 mi) north of Bobo-Dioulasso, and is itself about 163 square kilometres (63 sq mi) in size.