Lake Piso, also known as Lake Pisu and Fisherman's Lake, is an oblong tidal lagoon in Grand Cape Mount County in western Liberia, near the town of Robertsport. At an area of 103 km2 (40 sq mi), it is the largest lake in Liberia. Its name originates from a local term meaning "pigeon's hole" – a reference to the flocks of pigeons that once came to Lake Piso for water.