River, north-central Bolivia.
It rises in the Andes Mountains and in its upper course is sometimes known as Río Grande. It flows north to the Brazilian border, where it is joined by the Guaporé River ; it forms the border of Bolivia and Brazil as far north as Villa Bella, where it joins the Beni River to form the Madeira River , after a total course of about 1,200 mi (1,900 km). It is navigable to Guajará-Mirim, Braz.