From there it runs northeast, through the Ruvubu National Park, up to the Tanzanian border. After a stretch along the border, the Ruvubu crosses properly into Tanzania, before joining the Nyabarongo River on the Tanzania–Rwanda border near Rusumo Falls, to form the Kagera River.
The course of the Ruvubu river follows a northeast trajectory, passing through Ruvubu National Park and reaching the Tanzanian border. After crossing the border, it enters Tanzania and joins the Nyabarongo River at the border near Rusumo Falls to form the Kagera River.