BENI, a river of Bolivia, a tributary of the Madeira, rising in the elevated Cordilleras near the city of La Paz and at first known as the Rio de La Paz, and flowing east, and north-east, to a junction with the Mamoré at 10° 20' S. lat. to form the Madeira. Fully one-half of its length is through the mountainous districts of central Bolivia, where it is fed by a large number of rivers and streams from the snowclad peaks, and may be described as a raging torrent. Below Reyes its course is through the forest-covered hills and open plains of northern Bolivia, where some of the old Indian missions were located. The lower river is navigable for 217 m. from Reyes to the Esperanza rapids, 18 m. above its confluence with the Mamoré, where a fall of 20 ft. in a distance of 330 yds. obstructs free navigation. Its principal affluent is the Madre de Dios, or Mayu-tata, which rises in the eastern Cordilleras about 35 m. east of Cuzco, and flows in an east and north-east direction through northern Bolivia to a junction with the Bení 120 m. above its mouth. The principal tributaries of the Madre de Dios are the Inambari and Paucartambo, both large rivers, and the Chandless, Marcapata, and Tambopata. In length and size of its tributaries the Madre de Dios is a more important river than the Bení itself, and is navigable during the wet season to the foot of the Andes, 180 m. from Cuzco.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)