Lake Piso, Liberia's largest lake, is a 103 km² tidal lagoon in Grand Cape Mount County near Robertsport. Named after local pigeons that once frequented its waters, this brackish lake connects to the Atlantic Ocean via a narrow inlet and receives flow from several rivers. The area features islands like Massatin Island, home to monkeys and diverse bird species, earning it recognition as an Important Bird Area. Historically, it served as a WWII seaplane base and a refuge during Liberia's civil war. A designated nature reserve and wetland of international importance, the lake supports fishing, water sports, and diamond mining while remaining central to the Vai people's homeland.