River, northwest-central South America.
It rises in Peru and flows generally northeast through the rainforests of Peru and Brazil in one of the world's most meandering courses. In Brazil it joins the stretch of the Amazon River upstream from Manaus known as the Solimõ es River. At its mouth it divides into numerous branches. Most of its 1,995-mi (3,211-km) course is navigable, as are the many lakes formed near its shores. Rubber is gathered from forests along its course.