The Abuna River (Spanish Río Abuná, Portuguese Rio Abunã) is a river in South America. As a part of the Amazon Basin, it forms part of the border between northern Bolivia and north-western Brazil.The river has a total length of 375 km (234 mi). It is rising in several streams east of the Cordillera Oriental of the Peruvian Andes. The river is navigable for circa 320 km (200 mi) in its lower northeastern part. At Manoa it joins the Río Madeira, a tributary of the Amazon. Opposite the river mouth there is the town of Abunã on the Brazilian side of the confluence.