The Nyabarongo (or Nyawarungu) is a major river in Rwanda, part of the upper headwaters of the Nile. With a total length of 351 km (218 mi), it is the longest river entirely in Rwanda. It is extended 421 km (262 mi) in Lake Rweru including a 69 km (43 mi) upper course of Kagera River before joining into Ruvuvu River to form the Kagera River. The river begins its course at the confluence of the rivers Mbirurume and Mwogo in the South West of the country. These two rivers themselves begin in Nyungwe Forest, and are considered by some to be the most distant source of the Nile. From its start, Nyabarongo flows northward for 85 km (53 miles), and forms the border between the Western and Southern Provinces. At the confluence with the river Mukungwa, the river changes course and flows eastward for 12 km (7.5 miles), then to a more South Eastern course for the last 200 km (124 miles). For the longest stretch of this course, the river serves as the boundary between the Northern and Southern Provinces, then between the City of Kigali and the Southern Province, and lastly between the City of Kigali and the Eastern Province.
The river then before enters the Eastern Province and ends its course close to the border with Burundi. The Nyabarongo River empties both in Lake Rweru and Akagera river in a small but complicated Delta. The Akagera river outflows from Lake Rweru, a mere 1 km from the Nyabarongo delta. Almost all the branches of the Nyabarongo delta empty in the lake, however, one branch of the delta empties directly in the just formed Akagera river. The Akagera River eventually flows into Lake Victoria and forms the Nile.