Casamance River, river in western Africa, rising in southern Senegal and flowing west through the Casamance region, which lies between The Gambia (north) and Guinea-Bissau (south). The river receives various small tributaries and empties into the Atlantic Ocean after a course of 190 miles (300 km). Except for the tidal, salty 75-mile (120-kilometre) portion that is affected by the ocean, the river flows through broad, flat floodplains with luxuriant vegetation. There is a permanent flow as far upstream as Fafakourou (25 miles [40 km] northeast of Kolda). The Casamance makes a poor waterway, however, and even small boats can only proceed as far as Sédhiou (about 80 miles [130 km] inland).