The Rufiji River lies entirely within the African nation of Tanzania. The river is formed by the convergence of the Kilombero and Luwegu rivers. It is approximately 600 km (375 mi) long, with its source in southwestern Tanzania and its mouth on the Indian Ocean at a point between Mafia Island called Mafia Channel. Its principal tributary is the Great Ruaha River. It is navigable for about 100 km (60 mi).
The Rufiji is about 200 km (120 mi) south of Dar-es-Salaam. The river's delta contains the largest mangrove forest in the world.