perennial river rising in the Matagoro Mountains in southeastern Tanzania. Flowing eastward into the Indian Ocean at a point about 20 miles (32 km) north of Cape Delgado, the Ruvuma River forms the boundary between Tanzania and Mozambique for a length of 400 miles (650 km) from the coast and has a total length of about 475 miles (760 km). Its chief tributaries are the Lugenda, Lucheringo, Likonde, Muhuwesi, and Lumesule rivers. The Ruvuma River passes over several cataracts, so that it is navigable only by small craft up to the Upinda Rapids, about 60 miles (100 km) inland.