| Ucayali River | |
| Map: | Ucayalirivermap.png |
| Map Size: | 300 |
| Pushpin Map Size: | 300 |
| Subdivision Type1: | Country |
| Subdivision Name1: | Peru |
| Length: | 2238km (1,391miles)[1] 1460km (910miles)[2] |
| Discharge1 Min: | 3000m3/s[3] |
| Discharge1 Avg: | (Period of data: 1990-2006)13385m3/s[4] 13500m3/s(Confluence of Marañón: ~13800m3/s) |
| Discharge1 Max: | 28000m3/s |
| Source1: | confluence of the Tambo and Urubamba Rivers |
| Source1 Location: | Atalaya, Ucayali, Peru |
| Mouth: | Amazon River |
| Mouth Location: | confluence with Marañón River, Loreto, Peru |
| Basin Size: | 351549km2 |
| Discharge2 Location: | Pucallpa, Peru (Basin size: 260733km2 |
| Discharge2 Avg: | (Period of data: 1990-2006)8931.2m3/s |
The Ucayali River (Spanish; Castilian: Río Ucayali, pronounced as /es/) is the main headstream of the Amazon River. It rises about 110km (70miles) 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.
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 2669.9km (1,659miles) from the source of the Apurímac at Nevado Mismi to the confluence of the Ucayali and Marañón Rivers:
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 380km (240miles) of Lima, and the little steamer "Napo" found its way up the violent currents for 124km (77miles) above the junction with the Pachitea River, and as far as the Tambo River, 1240km (770miles) from the confluence of the Ucayali with the Amazon. The "Napo" then succeeded in ascending the Urubamba River 56km (35miles) upstream from its junction with the Tambo, to a point 320km (200miles) north of Cuzco.
The Ucayali's width varies from 400m–1200mm (1,300feet–3,900feetm), due to the large number of islands. The current runs from 5km/h6km/h, and a channel from 20m–50mm (70feet–160feetm) wide can always be found with a minimum depth of 1.5m (04.9feet). 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.
The 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.