The Amazon River
The Amazon River is the biggest river in the world by water volume by a huge margin. It carries roughly a fifth of all the river water on the planet at any moment. The Amazon stretches around 6,400 km across the top of South America, flowing from the high Andes mountains of Peru all the way to the Atlantic Ocean in northern Brazil.
- Length6,400 kmIn tied first place with the Nile
- Water flow209,000 m³/secRoughly 20% of all river water on Earth
- SourceAndes of PeruSnowmelt from high mountain glaciers
- MouthAtlantic OceanThrough a delta in northern Brazil
- Fish speciesOver 2,500More than the entire Atlantic Ocean
- Tributariesapprox. 1,100Many of which would themselves count as great rivers
How much water does the Amazon carry?
The Amazon carries more water than the next seven biggest rivers combined. The Nile, despite being just as long, carries only a small fraction.
The world's mightiest river
The Amazon River starts as small streams of snowmelt high in the Andes mountains of Peru. These streams join together to form bigger streams, then small rivers, then ever bigger rivers. By the time the Amazon reaches the Atlantic Ocean, it is so wide that you cannot see across it; in places it stretches more than 50 km from bank to bank in the wet season.
The flooded forest
Every year, the Amazon River floods huge areas of rainforest. The water level can rise by 15 metres or more in the wet season, turning the forest floor into an underwater world for months at a time. Fish swim between the tree trunks, eating fruit that falls from the branches. Many tree species have adapted to this regular flooding by producing seeds that float and grow in flooded soil. This flooded forest, called the várzea, is one of the most unusual ecosystems on Earth.
Wildlife of the river
The Amazon River and its tributaries hold more than 2,500 species of fish, more than in all of the Atlantic Ocean combined. The most famous include the arapaima (one of the biggest freshwater fish in the world, growing to over 3 metres long), the electric eel (which can stun prey with a 600-volt electric shock), the meat-eating piranha, and the freshwater pink river dolphin. There are also river turtles, anacondas (the heaviest snakes in the world), giant otters and capybaras (the biggest rodents on Earth).
Sailing the Amazon
The Amazon is one of the few rivers in the world where you can sail a full-sized ocean ship thousands of kilometres upstream. Iquitos, a city of around 400,000 people in northern Peru, sits 3,700 km from the river's mouth, but it is still on the Amazon. Iquitos is one of the largest cities in the world that you cannot reach by road. To get there, you fly or you take a boat.
Deeper dive: source debates, the Amazon basin and the reversal that built it
The "true source" of the Amazon has been debated for centuries. Different expeditions have nominated different small streams in different parts of the high Peruvian Andes. A 2014 expedition using GPS technology placed the most distant continuous source at the small Cordillera Rumi Cruz mountains, where a stream called the Mantaro begins approx. 5,170 metres above sea level. The accepted source rotates between several similar candidates depending on the criteria used (some count only continuously flowing streams; others count snowmelt streams that only flow part of the year).
The Amazon Basin (the area of land that drains into the river) is the largest in the world at around 7 million square km. Roughly 60% of it lies in Brazil, the rest in Peru, Colombia, Venezuela, Ecuador, Bolivia, Guyana, Suriname and French Guiana. The Amazon River system has over 1,100 named tributaries, including 17 that are themselves over 1,500 km long. The longest single tributary, the Madeira, is itself nearly 3,400 km long, longer than the Mississippi.
The Amazon has not always flowed eastward. Until around 11 million years ago, the river system actually flowed westward into the Pacific Ocean. The slow upward rise of the Andes mountains (caused by the Nazca tectonic plate sliding under the South American plate) eventually blocked the western route. Water built up in a vast inland sea before finally finding a new way out through low points in the eastern rim of the continent. The river reversed direction and began flowing east into the Atlantic. This reversal carried sediment from the rising Andes down across the Amazon Basin, where it gradually built up the broad lowland we see today. Most of the soil under the Amazon rainforest was once a piece of the Andes mountains.
The forest the river flows through is the Amazon Rainforest. The other contender for "longest river" is the Nile.