River, north-central Bolivia. It rises in the
Andes Mountains and in its upper course is sometimes known as Ro Grande. It flows north to the Brazilian border, where it is joined by the
Guapor 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 Guajar-Mirim, Braz.
For more information on Mamor River, visit Britannica.com.