Maranon River

Marañón River
Valley of the Marañón between Chachapoyas (Leimebamba) and Celendín
Countries	Ecuador, Peru
Source	Andes
Mouth	Amazon River
Length	1,737 km (1,079 mi)
Basin	358,000 km2 (138,225 sq mi)
Discharge
- average	16,708 m3/s (590,037 cu ft/s)
Map of the Amazon Basin with the Marañón River highlighted

The Marañón River (Spanish: Río Marañón, IPA: [ˈri.o maɾaˈɲon]) is the principal or mainstem source of the Amazon River, arising about 160 km to the northeast of Lima, Peru, and flowing through a deeply eroded Andean valley in a northwesterly direction, along the eastern base of the Cordillera of the Andes, as far as 5 degrees 36' southern latitude; from where it makes a great bend to the northeast, and cuts through the jungle Andes, until at the Pongo de Manseriche it flows into the flat Amazon basin. Although historically, the term "Marañon River" often was applied to the river all the way to the Atlantic Ocean, nowadays the Marañon River is generally thought to end at the confluence with the Ucayali River, after which most cartographers label the ensuing waterway the Amazon River.

The Marañón River is Peru's second longest river according to a 2005 statistical publication by the Instituto Nacional de Estadística e Informática.

The Marañon River was considered the source of the Amazon River starting with the 1707 map published by Padre Samuel Fritz, who indicated the great river “has its source on the southern shore of a lake that is called Lauricocha, near Huánuco." Fritz’ reasoning was based on the fact that the Marañon River is the largest river branch one encounters when journeying upstream, something clearly evident on his map. For most of the 18th–19th centuries and into the 20th century, the Marañon River was generally considered the source of the Amazon. The Marañon River continues to claim the title of the "mainstem source" or "hydrological source" of the Amazon due to its contribution of the highest annual discharge rates, a distinction similar to the Mississippi's "source" at/near Lake Itasca in Minnesota and the Nile's "source" at/near Lake Tana on the Blue Nile in Ethiopia.