River, central Peru.
Rising in the Andes Mountains , it is part of the headwaters of the Amazon River . It flows northwest at elevations of about 12,000 ft (3,650 m) and descends through jungles in unnavigable rapids and falls; emerging from the most spectacular of these rapids, the Pongo de Manseriche, it is only 575 ft (175 m) above sea level. For the rest of its 879-mi (1,415-km) course, it meanders eastward, receiving the Huallaga River and then joining the Ucayali River to form the Amazon.