Geography Facts About the Amazon River

Caitlin Dempsey


The Amazon River is one of longest and largest rivers in the world.  It is also an ancient river; the Amazon started 11 million years ago as a transcontinental river and took on its current form around 2.4 million years ago.   Coursing through the most biologically diverse biomes in the world, the Amazon is a critically important river system.  Here are some interesting geographical facts about the Amazon River.

The Amazon River located in South America is the world’s second longest river.  At 3,976 miles (6,400 km) in length, it only narrowly loses the title for the world’s longest river to the Nile River in Egypt, which is 4,132 miles (6,650 km) in length.

River with the Largest Drainage and Waterflow

The Amazon River is the largest in terms of drainage and waterflow.  The Amazon River has an average dischargeof roughly 7,381,000 cubic feet per second (209,000 cubic meters per seconds) with an outflow into the Atlantic Ocean.  This discharge is greater than the next seven rivers combined.  The Amazon also has the largest drainage basin in the world at 2,720,000 square miles (7,050,000 square kilometers), and accounts for one-fifth of the world’s total river flow.

Satellite image showing the changing river patterns of the Amazon River.  Image: NASA, public domain.
Satellite image showing the changing river patterns of the Amazon River. Image: NASA, public domain.

The vast width of the Amazon has earned it the nickname, The River Sea.  The width of the Amazon varies greatly.  During the low season, the river ranges from one to 6.2 miles in width.  During the wet season, the Amazon expands to widths of 30 miles (48 kilometers). Flooding usually occurs between June and October.

Free weekly newsletter

Fill out your e-mail address to receive our newsletter!

Flowing through South America, the countries of Brazil, Peru, Bolivia, Colombia, Ecuador, Venezuela, Guyanaare in its catchment basin.  The Amazon Basin covers 40 percent of South America and is the largest in the world.

Origins of the Amazon River

The Amazon River originates from a glacial stream from a peak, called Nevado Mismifound an elevation of 18,363 feet (5,597 meters) in the Peruvian Andes. A simple wooden cross on the peak marks the most distant source of the Amazon River.

The glacial stream at Mismi is the origination point of the Amazon River, marked by a cross. Photo: Jialiang Gao, MediaWiki Commons, CC BY-SA 3.0
The glacial stream at Mismi is the origination point of the Amazon River, marked by a cross. Photo: Jialiang Gao,, MediaWiki Commons, CC BY-SA 3.0

The Ancient Beginnings of the Amazon River

The Amazon River region is composed of Precambrian fragments.  The Sierra de Carajás, in the Central Amazon province is the most important mineral province in Brazil. Its “greenstone belts” are about 3 billion years old, and represent the oldest rocks in the Amazon craton. (

During the Proterozoic, the main Amazon River flowed from east to west, emptying into the Pacific. Its source was in present day Africa.  After the collapse and the opening of the Atlantic during the Mesozoic, the South American Plate moved westward, where the Pacific Plate collided with Nazca, a region in the southern coast of Peru (Ward, P. 1995)

This collision lifted the Andes and interrupted the flow of the Amazon to the Pacific. Subsequently, large lakes were formed in the eastern part of the Andes, including the Belterra. A slight inclination of the South American continent to the east, led to the reversal of the course of the Amazon toward the Atlantic. During the Cenozoic, the Amazon and its tributaries, gradually carved a basin of the Amazon and today comprises plateaus, plains and valleys.

The Amazon Has Over 1,100 Tributaries

The Amazon has over 1,100 tributaries (smaller streams or rivers that branch off from the main river).  Of those tributaries, 17 are longer than 930 miles (1,500 kilometers) long.  The three longest tributaries are: Madeirawhich runs through Bolivia and Brazil and is 2,020 miles (3,250 km) long, Purús (running through Peru and Brazilat 1,995 miles (3,211 km) long, and Yapura (running through Colombia and Brazilat 1,750 miles (2,820 km) in length.

Map showing the Amazon River drainage basin. Amazon river is highlighted in bold. Map: Kmusser, MediaWiki Commons, CC BY-SA 3.0
Map showing the Amazon River drainage basin and the river’s tributaries. Amazon river is highlighted in bold. Map: Kmusser, MediaWiki Commons, CC BY-SA 3.0

The Amazon flows through the Amazon Rainforest, an area considered to be the most biologically diverse in the world. The exact number varies depending on the source, but experts estimate there are anywhere from 2,500 to 5,000 species of fish in the Amazon basin.  New species of fish are discovered every year in the basin.  The Amazon river dolphin is the largest river dolphin the world, growing up to 8 feet 6 inches inches (2.6 meters) in length.  The Anaconda, one of the world’s largest species of snake, makes its home in the Amazon River.  Piranha, a sharp-tooth fish that eats meat and caiman, a reptile related to alligators also inhabit the waters of the Amazon.

One of the longest rivers in the world, the Amazon River contains more water than any other river in the world.  Reaching from the Andes in Peru to the Atlantic ocean, in Brazil, the reach of the Amazon River covers an enormous area, occupying 40 percent of South America.

Which River is Longer: The Amazon or the Nile River?

If a group of Brazilian scientists get their way, the answer to “What is the longest river in the world” may no longer be the Nile.  An expedition by scientists are said to have discovered that the source of the Amazon is really in the South of Peru which, if true, gives the Amazon a calculated length of 6,800km (4,250 miles).  The Nile, by comparison is 6,695km in length.

Guido Gelli, director of science at the Brazilian Institute of Geography and Statistics, told the Brazilian network TV Globo that today it could already be considered as a fact that the Amazon was the longest river in the world.

This new measurement is backed by the findings of a separate Pan-Amazon Project, developed by five scientists from the Remote Sensing Division of the Brazilian National Space Research Institute (INPE) who used satellite imagery to compare the lengths of both the Nile and the Amazon rivers.  “We measured the Amazon and the Nile. There are final analyses to be done, but we can affirm that the former is longer than the latter,” study coordinator and geologist, Paulo Martini told Radiobrás, Brazil’s state news agency.


Amazon river once flowed in opposite direction. (2006, October 24). – News and Articles on Science and Technology.

Liu, S., Lu, P., Liu, D., Jin, P., & Wang, W. (2009). Pinpointing the sources and measuring the lengths of the principal rivers of the world. International Journal of Digital Earth2(1), 80-87.

Photo of author
About the author
Caitlin Dempsey
Caitlin Dempsey is the editor of Geography Realm and holds a master's degree in Geography from UCLA as well as a Master of Library and Information Science (MLIS) from SJSU.