 The watershed between the major Congo and Nile drainage basins runs from north to south through Rwanda, with around 80 percent of the country's area draining into the Nile and 20 percent into the Congo via the Rusizi River.The country's longest river is the Nyabarongo, which rises in the south-west, flows north, east, and southeast before merging with the Akanyaru to form the Akagera; the Akagera then flows due north along the eastern border with Tanzania.The Nyabarongo-Akagera eventually drains into Lake Victoria, and its source in Nyungwe Forest is a contender for the as-yet undetermined overall source of the Nile.