Two candidates for a single source
Pinning down where a river as vast as the Amazon "starts" turns out to be a genuinely contested question, not a settled fact with a marker on a map. The most widely cited source is a spring on the slopes of Nevado Mismi, a peak in Peru's Arequipa region, identified by a 1996 Polish and Peruvian expedition led by Jacek Palkiewicz. It built on a nearby source Loren McIntyre had identified for National Geographic in 1971, and a separate National Geographic GPS expedition returned to the area in 2000. Water from that spring flows into the Apurímac River, then the Ucayali, before joining the main Amazon channel in northern Peru.
A rival claim, published in 2014 by James Contos and Nicholas Tripcevich in the journal Area, argues that the true source is instead a stream feeding the Mantaro River, further north and measurably longer: roughly 809 km down the Mantaro against roughly 734 km down the Apurímac before the two paths converge. Contos and Tripcevich note themselves that the Mantaro headwaters run dry for several months each year, which is the strongest argument against treating that stream as the permanent source. Neither claim has been formally adopted as the single, uncontested answer, and the 2014 paper has not been adopted as the final word either. This site follows the more widely cited Nevado Mismi source, as the Nile's own headwater dispute in Rwanda and Burundi is followed on the Nile explainer: named, but honestly presented as contested.
From the Andes to the Atlantic
Whichever headwater is credited, the river's overall path is not in dispute. It falls from the Andes, gathers the Marañón and Ucayali into the main Amazon channel in Peru, then flows east across Brazil, widening as it absorbs huge tributaries such as the Rio Negro and the Madeira. Near its mouth the river splits around Marajó Island, roughly the size of Switzerland and the world's largest fluvio-maritime island, the kind formed where a river meets the sea, before reaching the Atlantic Ocean near the Brazilian port city of Belém. There is no true delta in the usual sense: much of the flow discharges directly into the ocean through a wide estuary, and the river's fresh water is detectable far out at sea.
A source-to-sea route
Longer than the Nile, depending who measured it
For decades the conventional figure for the Amazon's length was about 6,400 km, which put it just behind the Nile. That changed in July 2008, when Brazil's national space research institute, INPE, published a satellite-based remeasurement that traced the river to a headwater further upstream than earlier surveys had used and put the length at roughly 6,992 km. A peer-reviewed 2009 study using different rules reached the opposite conclusion, 6,575 km for the Amazon against 7,088 km for the Nile, which is a fair measure of how unsettled the question is. If that figure is accepted, the Amazon is longer than the Nile's approximately 6,650 km. Most encyclopedias and atlases still credit the Nile as the world's longest river, as the Nile explainer on this site lays out, because the dispute ultimately comes down to where each river's headwater is defined to begin and no single expedition has been accepted by all sides as the final word. What is not disputed is the Amazon's volume: no other river carries close to as much water.
A basin shared by nine territories
The Amazon basin, the largest drainage basin on Earth at roughly 7 million square kilometers, spans Brazil, Peru, Colombia, Bolivia, Ecuador, Venezuela, Guyana, Suriname, and French Guiana. Eight of those are sovereign countries; French Guiana is an overseas department of France rather than an independent state, similar to how French Guiana sits outside the usual count of South American countries. Brazil holds by far the largest share of the basin, followed by Peru, but rainfall across the entire span, not just Brazil, is what fills the river.
Quick facts
| Measure | Figure |
|---|---|
| Most cited source | Nevado Mismi, Arequipa region, Peru (Andes) |
| Rival source claim | A headwater of the Mantaro River, Peru |
| Mouth | Atlantic Ocean, near Belém, Brazil, beside Marajó Island |
| Length | About 6,400 km by the conventional measure; about 6,992 km per INPE's 2008 remeasurement |
| Average discharge | Roughly 209,000 to 224,000 cubic meters per second, more than the next several largest rivers combined |
| Basin countries | 9: Brazil, Peru, Colombia, Bolivia, Ecuador, Venezuela, Guyana, Suriname, and French Guiana (a French territory) |