The Ucayali River (, ) is the main headstream of the Amazon River. It rises about north of Lake Titicaca, in the Arequipa region of Peru and becomes the Amazon at the confluence of the Marañón close to Nauta city. The city of Pucallpa is located on the banks of the Ucayali. Description The Ucayali, together with the Apurímac River, the Ene River and the Tambo River, is today considered the main headwater of the Amazon River, totaling a length of from the source of the Apurímac at Nevado Mismi to the confluence of the Ucayali and Marañón Rivers: Apurímac River (total length): Ene River (total length): Tambo River (total length): Ucayali River (confluence with Tambo River to confluence with the Marañón): Exploration The Ucayali was first called San Miguel, then Ucayali, Ucayare, Poro, Apu-Poro, Cocama and Rio de Cuzco. Peru has organised many costly and ably-conducted expeditions to explore it. One of them (1867) claimed to have reached within of Lima, and the little steamer "Napo" found its way up the violent currents for above the junction with the Pachitea River, and as far as the Tambo River, from the confluence of the Ucayali with the Amazon. The "Napo" then succeeded in ascending the Urubamba River upstream from its junction with the Tambo, to a point north of Cuzco. Navigation Its width varies from , due to the large number of islands. The current runs from , and a channel from wide can always be found with a minimum depth of . There are five difficult passes, due to the accumulation of trees and rafts of timber. Sometimes large rocks which have fallen from the mountains and spread over the river-bed cause whirlpools. National Reserve Ucayali is home to the Amazon river dolphin, giant otter, and the Amazonian manatee, which are abundant in Pacaya-Samiria National Reserve, close to Nauta. The southeastern border of the reserve is formed by the lower Ucayali River. The river gives its name to the Ucayali Region of Peru and the Ucayali Province of the Loreto Region. References External links Rivers of Peru Tributaries of the Amazon River Rivers Rivers of Ucayali Region Upper Amazon