The Malagarasi River is Tanzania's second longest river. It empties into the eastern side of Lake Tanganyika about 25 miles south of Kigoma, and is one of the lake's primary inflows. The Malagarasi pre-dates Lake Tanganyika and was formerly a tributary of the Congo River to its west. The first 80 kilometres of the river forms the international boundary between Tanzania and Burundi. Main tributaries are Ugalla River, Gombe River, Moyowosi River, Ruchugi River and Nguya River.