Apurímac River (total length): 730.7 km (454.0 mi)
Ene River (total length): 180.6 km (112.2 mi)
Tambo River (total length): 158.5 km (98.5 mi)
Ucayali River (confluence with Tambo River to confluence with the Marañón): 1,600.1 km (994.3 mi)
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 380 km (240 mi) of Lima, and the little steamer "Napo" found its way up the violent currents for 124 km (77 mi) above the junction with the Pachitea River, and as far as the Tambo River, 1,240 km (770 mi) from the confluence of the Ucayali with the Amazon. The "Napo" then succeeded in ascending the Urubamba River 56 km (35 mi) upstream from its junction with the Tambo, to a point 320 km (200 mi) north of Cuzco.
Navigation
The Ucayali's width varies from 400–1,200 metres (1,300–3,900 ft), due to the large number of islands. The current runs from 5–6 kilometres per hour (3.1–3.7 mph), and a channel from 20–50 metres (66–164 ft) wide can always be found with a minimum depth of 1.5 m (4.9 ft). 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 across the riverbed cause whirlpools.
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