Senegal River, a river in western Africa. It is formed by the junction of the Bafing and Bakoy rivers in Mali, and flows generally northwestward along the Mauritania-Senegal boundary to the Atlantic Ocean near Saint-Louis, Senegal. The water level of the river fluctuates widely with the wet and dry seasons. Virtually the entire 650-mile course is navigable by small boats during high water, only the lower one-fourth during low water.