River, northwestern South America.
Rising in southwestern Colombia, it is about 980 mi (1,575 km) long and flows southeast through tropical rainforests, where it forms a large section of the border between Peru and Colombia. It crosses the border into Brazil, where it is known as the Içá and empties into the Amazon River . It is navigable for almost its entire length and is a major transport route, especially for the rubber produced in the region.