The brackish water lake borders the Cape Mount peninsula, and is connected to the Atlantic Ocean by a narrow inlet known locally as the "bar mouth". Various rivers empty into Lake Piso, including Mole Creek and Mafa River, which discharges at the 'bar mouth'. There are a number of islands in the lake, including Massatin Island, which offered a haven for monkeys and birds species, it also served as temporary refuge for some Liberians during the Liberian Civil War.