headwater tributary of the Amazon in southeastern Peru and northwestern Bolivia. It flows from the Cordillera de Carabaya, easternmost range of the Andes, in Peru, and meanders generally eastward past Puerto Maldonado to the Bolivian border. There it turns northeastward and crosses the remote tropical rain forest of northwestern Bolivia. It joins the Beni River at Riberalta in Bolivia after a course of more than 700 miles (1,100 km). Numerous tributaries, including the Manu, Colorado Arana, Pariamanu, and Tambopata, flow into the main river, the upper course of which can be navigated by small craft. Below the rapids at Puerto Heath, on the Peru-Bolivia border, the Madre de Dios again becomes an important transportation artery. Rubber is gathered from the dense tropical rain forest along the river's banks. The basin is sparsely settled and in parts of the upper course is uninhabited.