The Amazon River ( ; ; (US); (UK)) of South America is the largest river in the world by volume, with a total river flow greater than the next eight largest rivers combined. The Amazon, which has the largest drainage basin in the world, accounts for approximately one-fifth of the world's total river flow. During the wet season, parts of the Amazon exceed in width. Because of its vast dimensions, it is sometimes called The River Sea. At no point is the Amazon crossed by bridges. This is not because of its huge dimensions; in fact, for most of its length, the Amazon's width is well within the capability of modern engineers to bridge. However, the bulk of the river flows through tropical rainforest, where there are few roads and even fewer cities, so there is no need for crossings.

While the Amazon is the largest river in the world by most measures, the current consensus within the geographic community holds that the Amazon is the second longest river, just slightly shorter than the Nile. However, some scientists, particularly from Brazil and Peru, dispute this (see section below).

The Amazon Basin, the largest drainage basin in the world, covers about 40 percent of South America, an area of approximately . It gathers its waters from 5 degrees north latitude to 20 degrees south latitude. Its most remote sources are found on the inter-Andean plateau, just a short distance from the Pacific Ocean.

The area covered by the water of the Amazon River and its tributaries more than triples over the course of a year. In an average dry season, of land are water-covered, while in the wet season, the flooded area of the Amazon Basin rises to .

The quantity of water released by the Amazon to the Atlantic Ocean is enormous: up to per second in the rainy season. The Amazon is responsible for about 20% of the total volume of freshwater entering the oceans worldwide . Offshore of the mouth of the Amazon, potable water can be drawn from the ocean while still out of sight of the coastline, and the salinity of the ocean is notably lower out to sea.

Origins

The Upper Amazon has a series of major river systems in Peru and Ecuador, some of which flow into the Marañón and others directly into the Amazon proper. Among others, these include the following rivers: Morona, Pastaza, Nucuray, Urituyacu, Chambira, Tigre, Nanay, Napo, Huallaga, and Ucayali. The headstreams of the Marañón—which for many years had been seen as the origin of the Amazon—flow from high above central Peru's Lake Lauricocha, from the glaciers in what is known as the Nevado de Yarupa. Rushing through waterfalls and gorges in an area of the high jungle called the pongo, the Marañón River flows about from west-central to northeast Peru before it combines with the Ucayali River, just below the provincial town of Nauta, to form the Amazon River.

The most distant source of the Amazon was firmly established in 1996, 2001 and 2007 as a glacial stream on a snowcapped peak called Nevado Mismi in the Peruvian Andes, roughly west of Lake Titicaca and southeast of Lima. The waters from Nevado Mismi flow into the Quebradas Carhuasanta and Apacheta, which flow into the Río Apurímac which is a tributary of the Ucayali which later joins the Marañón to form the Amazon proper. (While this is the point at which most geographers place the beginning of the Amazon proper, in Brazil the river is known at this point as the Solimões das Águas). Soon thereafter the darkly colored waters of the Rio Negro meet the sandy colored Rio Solimões, and for over these waters run side by side without mixing.

After the confluence of Río Apurímac and Ucayali, the river leaves Andean terrain and is instead surrounded by floodplain. From this point to the Marañón, some , the forested banks are just out of water, and are inundated long before the river attains its maximum flood-line. The low river banks are interrupted by only a few hills, and the river enters the enormous Amazon Rainforest.

The river systems and flood plains in Brazil, Peru, Ecuador, Colombia and Venezuela whose waters drain into the Solimões and its tributaries are called the "Upper Amazon".The Amazon River proper runs mostly through Brazil and Peru, and it has tributaries reaching into Venezuela, Colombia, Ecuador, and Bolivia.

Flooding

Not all of the Amazon's tributaries flood at the same time of the year. Many branches begin flooding in November, and may continue to rise until June. The rise of the Rio Negro starts in February or March, and it also begins to recede in June. The Madeira rises and falls two months earlier than most of the rest of the Amazon.

The average depth of the river in the height of the rainy season is and the average width can be nearly .

The main river (which is between approximately one and six miles (10 km) wide) is navigable for large ocean steamers to Manaus, upriver from the mouth. Smaller ocean vessels of 3,000 tons or 9,000 tons and draft can reach as far as Iquitos, Peru, from the sea. Smaller riverboats can reach higher as far as Achual Point. Beyond that, small boats frequently ascend to the Pongo de Manseriche, just above Achual Point.

Geography

At some points, for long distances, the river divides into two main streams with inland and lateral channels, all connected by a complicated system of natural canals, cutting the low, flat igapo lands, which are never more than above low river, into many islands.

From the town of Canaria at the great bend of the Amazon to the Negro, only very low land is found, resembling that at the mouth of the river. Vast areas of land in this region are submerged at high water, above which only the upper part of the trees of the sombre forests appear. Near the mouth of the Rio Negro to Serpa, nearly opposite the river Madeira, the banks of the Amazon are low, until approaching Manaus, they rise to become rolling hills. At Óbidos, a bluff above the river is backed by low hills. The lower Amazon seems to have once been a gulf of the Atlantic Ocean, the waters of which washed the cliffs near Óbidos.

Only about 10% of the water discharged by the Amazon enters the mighty stream downstream of Óbidos, very little of which is from the northern slope of the valley. The drainage area of the Amazon Basin above Óbidos city is about 5 million square kilometres (2,000,000 sq mi), and, below, only about 1 million square kilometres (400,000 sq mi or around 20%), exclusive of the 1.4 million square kilometres (540,000 sq mi) of the Tocantins basin.

In the lower reaches of the river, the north bank consists of a series of steep, table-topped hills extending for about from opposite the mouth of the Xingu as far as . These hills are cut down to a kind of terrace which lies between them and the river.

On the south bank, above the Xingu, an almost-unbroken line of low bluffs bordering the flood-plain extends nearly to Santarém, in a series of gentle curves before they bend to the south-west, and, abutting upon the lower Tapajós, merge into the bluffs which form the terrace margin of the Tapajós river valley.

Mouth

The definition of what exactly and how wide is the mouth of the Amazon is a matter of dispute, because of the area's peculiar geography. Most particularly, sometimes the Pará River is included, whereas sometimes it is just considered the independent lower reach of the Tocantins River. The Pará river estuary alone is wide. The Pará and the Amazon are connected by a series of river channels called furos near the town of Breves; between them lies Marajó, an island almost the size of Switzerland that is the world's largest combined river/sea island.

If the Pará river and the Marajó island ocean frontage are included, the Amazon estuary is some wide. In this case, the width of the mouth of the river is usually measured from Cabo Norte, in the Brazilian state of Amapá, to Ponta da Tijoca near the town of Curuçá, in the state of Pará. By this criterion, the Amazon is wider at its mouth than the entire length of the River Thames in England.

A more conservative measurement excluding the Pará river estuary, from the mouth of the Araguari River to Ponta do Navio on the northern coast of Marajó, would still give the mouth of the Amazon a width of over . If only the river's main channel is considered, between the islands of Curuá (state of Amapá) and Jurupari (state of Pará, the width falls to just about - but that is still impressive for any river.

Tidal bore (pororoca)

The tension between the river's strong push and the Atlantic tides causes a phenomenon called a tidal bore, a powerful tidal wave that flows rapidly inland from the sea up the Amazon mouth and nearby coastal rivers several times a year at high tide. Tidal bores also occur in other river mouths around the world, but the Amazon's are among the world's highest and fastest, probably second only to those of Qiantang River in China. In the Amazon, the phenomenon is locally known as the pororoca.

The pororoca occurs especially where depths do not exceed . It starts with a very loud roar, constantly increasing, and advances at the rate of with a breaking wall of water high that may travel violently several kilometres up the Amazon and other rivers close to its mouth. It is particularly intense in the rivers of the coast of the state of Amapá north of the mouth of the Amazon, such as the Araguari River, but can be observed in Pará rivers as well.

The bore is the reason the Amazon does not have a protruding delta; the ocean rapidly carries away the vast volume of silt carried by the Amazon, making it impossible for a delta to grow past the shoreline. The region also has very high tides, sometimes reaching and has become a popular spot for river surfing.

Wildlife

More than one-third of all species in the world live in the Amazon Rainforest, a giant tropical forest and river basin with an area that stretches more than 5.4 million square kilometres (2.1 million sq mi), and is the richest tropical forest in the world. The Amazon River has over 3,000 recognized species of fish and that number is still growing.

Along with the Orinoco, the river is one of the main habitats of the boto, also known as the Amazon River Dolphin (Inia geoffrensis). It is the largest species of river dolphin, and it can grow to lengths of up to . The boto is the subject of a very famous legend in Brazil about a dolphin that turns into a man and seduces maidens by the riverside. The tucuxi (Sotalia fluviatilis), also a dolphin species, is found both in the rivers of the Amazon Basin and in the coastal waters of South America.

Also present in large numbers is the notorious piranha, a carnivorous fish which congregates in large schools, and may attack livestock and even humans. However, only a few of its species are known to attack humans, most notably Pygocentrus nattereri, the Red-bellied Piranha.

The bull shark (Carcharhinus leucas) has been reported up the Amazon River at Iquitos in Peru. The arapaima, known in Brazil as the pirarucu (Arapaima gigas), is a South American tropical freshwater fish. It is one of the largest freshwater fish in the world, reportedly with a maximum length in excess of and weight up to . Another Amazonian freshwater fish is the arowana (or aruanã in Portugeuse), such as the Silver arowana (Osteoglossum bicirrhosum), which is also a predator and very similar to the arapaima, but only reaches a length of maximum . The candirú are a number of genera of parasitic, freshwater catfish in the family Trichomycteridae; all are native to the Amazon River. They sometimes attack humans and have been known to enter the urethras of bathers. The electric eel (Electrophorus electricus) is also found in the river.

The anaconda snake is found in shallow waters in the Amazon Basin. One of the world's largest species of snake, the anaconda spends most of its time in the water, with just its nostrils above the surface. In addition to the thousands of species of fish, the river supports crabs, algae, and turtles.

Colonial encounters with the Amazon

During what many archaeologists call the formative period, Amazonian societies were deeply involved in the emergence of South America's highland agrarian systems, and possibly contributed directly to the social and religious fabric constitutive of the Andean civilizational orders.

In 1515, Vicente Yáñez Pinzón was the first European to sail into the river. Pinzón called the river flow Río Santa María del Mar Dulce, later shortened to Mar Dulce (literally, sweet sea, because of its freshwater pushing out into the ocean). For 350 years after the first European encounter of the Amazon by Pinzón, the Portuguese portion of the basin remained an untended former food gathering and planned agricultural landscape occupied by the indigenous peoples who survived the arrival of European diseases. There is ample evidence for complex large-scale, pre-Columbian social formations, including chiefdoms, in many areas of Amazonia (particularly the inter-fluvial regions) and even large towns and cities. For instance the pre-Columbian culture on the island of Marajó may have developed social stratification and supported a population of 100,000 people. The Native Americans of the Amazon rain forest may have used Terra preta to make the land suitable for the large scale agriculture needed to support large populations and complex social formations such as chiefdoms.

One of Gonzalo Pizarro's lieutenants, Francisco de Orellana, during his 1541 expedition, east of Quito into the South American interior in search of El Dorado and the Country of the Cinnamon was ordered to explore the Coca River and return when the river ended. When they arrived to the confluence to the Napo River, his men menaced to mutiny if they did not continue. On 26 December 1541, he accepted to be elected chief of the new expedition and to conquest new lands in name of the king. The 49 men began to build a bigger ship for riverine navigation. During their navigation on Napo River they were threatened constantly by the Omaguas. They reached Negro River on 3 June 1542 and finally arrived to the Amazon River, that was so named because they were allegedly attacked by fierce female warriors like the mythological Amazons. The Icamiaba natives dominated the area close to the Amazon River, rich in gold. When Orellana went down the river in search of gold, descending from the Andes (in 1541), the Amazon was called Grande Río ("Large River"), Mar Dulce ("Sweet[water] Sea") or Río de la Canela ("Cinnamon River," because of the great cinnamon trees that Orellana claimed to have found there - in spite of cinnamon being an Asian plant impossible to be found growing in the wild in 16th-century South America). Orellana narrated the belligerent victory of the Icamiaba women against the Spanish invaders to Charles V, Holy Roman Emperor, who, inspired by the Greek Amazons, baptized the river as Amazonas, the name by which it is still known in both Spanish and Portuguese.

In 1637–47 the Portuguese explorer Pedro Teixeira was the first European to ascend the river from Belém (near the mouth of the Amazon) to Quito, part of the Spanish Viceroyalty of Peru, and then to return the same way. Teixeira's expedition was massive - some 2000 people in 37 large canoes. From 1648 to 1652, António Raposo Tavares lead one of the longest known expeditions from São Paulo to the mouth of the Amazon, investigating many of its tributaries, including the Rio Negro, and covering a distance of more than .

In what is currently Brazil, Ecuador, Bolivia, Colombia, Peru, and Venezuela, a number of colonial and religious settlements were established along the banks of primary rivers and tributaries for the purpose of trade, slaving and evangelization among the indigenous peoples of the vast rain forest. Father Fritz, apostle of the Omaguas, established some forty mission villages. Charles Marie de La Condamine accomplished the first scientific exploration of the Amazon River.

The Cabanagem, one of the bloodiest regional wars ever in Brazil, which was chiefly directed against the white ruling class, reduced the population of Pará from about 100,000 to 60,000.

The total population of the Brazilian portion of the Amazon Basin in 1850 was perhaps 300,000, of whom about two-thirds comprised by Europeans and slaves, the slaves amounting to about 25,000. The Brazilian Amazon's principal commercial city, Pará (now Belém), had from 10,000 to 12,000 inhabitants, including slaves. The town of Manáos, now Manaus, at the mouth of the Rio Negro, had a population between 1,000 to 1,500. All the remaining villages, as far up as Tabatinga, on the Brazilian frontier of Peru, were relatively small.

Post-colonial history

On 6 September 1850, the emperor, Pedro II, sanctioned a law authorizing steam navigation on the Amazon, and gave the Viscount of Mauá (Irineu Evangelista de Sousa) the task of putting it into effect. He organized the "Companhia de Navegação e Comércio do Amazonas" in Rio de Janeiro in 1852; and in the following year it commenced operations with three small steamers, the Monarch, the Marajó and Rio Negro.

At first, navigation was principally confined to the main river; and even in 1857 a modification of the government contract only obliged the company to a monthly service between Pará and Manaus, with steamers of 200 tons cargo capacity, a second line to make six round voyages a year between Manaus and Tabatinga, and a third, two trips a month between Pará and Cametá. This was the first step in opening up the vast interior.

The success of the venture called attention to the opportunities for economic exploitation of the Amazon, and a second company soon opened commerce on the Madeira, Purus and Negro; a third established a line between Pará and Manaus; and a fourth found it profitable to navigate some of the smaller streams. In that same period, the Amazonas Company was increasing its fleet. Meanwhile, private individuals were building and running small steam craft of their own on the main river as well as on many of its tributaries.

On 31 July 1867 the government of Brazil, constantly pressed by the maritime powers and by the countries encircling the upper Amazon basin, especially Peru, decreed the opening of the Amazon to all flags; but limited this to certain defined points: Tabatinga — on the Amazon; Cametá — on the Tocantins; Santarém — on the Tapajós; Borba — on the Madeira, and Manaus — on the Rio Negro. The Brazilian decree took effect on 7 September 1867.

Thanks in part to the mercantile development associated with steamboat navigation, coupled with the internationally driven demand for natural rubber (1880-1920), Manáos (now Manaus) and Pará (now Belém) in (Brazil), and Iquitos, Peru became thriving, cosmopolitan centers of commerce and spectacular — albeit illusory — "modern" "urban growth". This was particularly the case for Iquitos during its late 19th and early 20th century Rubber Bonanza zenith when this dynamic boomtown was known abroad as the St. Louis of the Amazon.

The first direct foreign trade with Manaus was commenced around 1874. Local trade along the river was carried on by the English successors to the Amazonas Company — the Amazon Steam Navigation Company — as well as numerous small steamboats, belonging to companies and firms engaged in the rubber trade, navigating the Negro, Madeira, Purus and many other tributaries, such as the Marañón to ports as distant as Nauta, Peru. The Amazon Steam Navigation Company had 38 vessels.

By the turn of the 20th century, the principal exports of the Amazon Basin were India-rubber, cacao, Brazil nuts and a few other products of minor importance, such as pelt and exotic forest produce (resins, barks, woven hammocks, prized bird feathers, live animals, etc.) and extracted goods (lumber, gold, etc.).

20th century concerns

Four centuries after the European discovery of the Amazon river, the total cultivated area in its basin was probably less than , excluding the limited and crudely cultivated areas among the mountains at its extreme headwaters. This situation changed dramatically during the 20th century.

Wary of foreign exploitation of the nation's resources, Brazilian governments in the 1940s set out to develop the interior, away from the seaboard, where foreigners owned large tracts of land. The original architect of this expansion was President Getúlio Vargas, with the demand for rubber from the Allied forces in World War II providing funding for the drive.

In 1960, the construction of the new capital city of Brasília in the interior also contributed to the opening up of the Amazon Basin. A large-scale colonization program saw families from Northeastern Brazil relocated to the forests, encouraged by promises of cheap land. Many settlements grew along the road from Brasilia to Belém, but rainforest soil proved difficult to cultivate.

Still, long-term development plans continued. Roads were cut through the forests, and in 1970, the work on the Trans-Amazonian highway (Transamazônica) network began. The network's three pioneering highways were completed within ten years, but never fulfilled their promise. Large portions of the Trans-Amazonian and its accessory roads, such as BR-319 (Manaus-Porto Velho), are derelict and impassable in the rainy season.

With a current population of 1.8 million people, Manaus is the Amazon’s largest city. Manaus alone represents approximately 50% of the population of the Brazilian state of Amazonas, which is the largest state. The racial makeup of the city is 64% Pardo (Mulatto and mestizo) and 32% White.

Dispute regarding length

While debate as to whether the Amazon or the Nile is the world's longest river has gone on for many years, the historic consensus of geographic authorities has been to regard the Amazon as the second longest river in the world, with the Nile being the longest. However, the Amazon has been measured by different geographers as being anywhere between 6,259 and 6,800 kilometres long. The Nile is reported to be anywhere from 5,499 to 6,690 kilometres The differences in these measurements often result from the use of different definitions.

A study by Brazilian scientists claimed that the Amazon is actually longer than the Nile. Using Nevado Mismi, which in 2001 was labeled by the National Geographic Society as the Amazon's source, these scientists have made new calculations of the Amazon's length. They now estimate that the Amazon is longer than the Nile, and Guido Gelli, director of science at the Brazilian Institute of Geography and Statistics (IBGE), told the Brazilian TV network Globo in June 2007 that it could be considered as a fact that the Amazon was the longest river in the world. However, other geographers have had access to the same data since 2001, and a consensus has yet to emerge to support the claims of these Brazilian scientists.

Major tributaries

The Amazon has over 1,100 tributaries in total, 17 of which are over . Some of the more notable ones are:

• Branco
• Casiquiare canal
• Caqueta River
• Huallaga
• Putumayo
• Javary
• Jurua
• Madeira
• Marañón
• Morona
• Nanay
• Napo

• Negro
• Pastaza
• Purus
• Tambo
• Tapajós
• Tigre
• Tocantins
• Trombetas
• Ucayali
• Xingu
• Yapura

Longest rivers in the Amazon system

1. - Amazon, South America
2. - Purus, Peru / Brazil, (2,948 km) (3,210 km)
3. - Madeira, Bolivia / Brazil
4. - Yapura, Colombia / Brazil
5. - Tocantins, Brazil, (2,416 km) (2,640 km)
6. - Araguaia, Brazil (tributary of Tocantins)
7. - Juruá, Peru / Brazil
8. - Rio Negro, Brazil/ Venezuela / Colombia
9. - Xingu, Brazil
10. - Tapajós, Brazil
11. - Guaporé, Brazil / Bolivia (tributary of Madeira)
12. - Ucayali River, Peru
13. - Içá , South America
14. - Marañón, Peru
15. - Teles Pires, , Brazil (tributary of Tapajós)
16. - Iriri, Brazil (tributary of Xingu)
17. - Juruena, Brazil (tributary of Tapajós)
18. - Tapajós, Brazil
19. - Madre de Dios, Peru / Bolivia (tributary of Madeira)
20. - Huallaga, Peru (tributary of Marañón)

Expeditions

The Amazon River is currently being walked from source to sea by Ed Stafford (UK), having started in April 2008. It is believed to be the first navigation of the Amazon on foot.

References

1. Tom Sterling: Der Amazonas. Time-Life Bücher 1979, 8th German Printing, p. 19
2. Source of the Amazon River Identificated (Jacek Palkiewicz)
3. Explorers Pinpoint Source of the Amazon (National Geographic News)
4. Amazon river 'longer than Nile' (BBC news) (2007-06-16)
5. Amazon uk.encarta.msn.com. Retrieved 1 October 2006. Archived 2009-10-31.
6. Amazon rainforest fact sheet
7. Megafishes Project to Size Up Real "Loch Ness Monsters". National Geographic.
8. Candiru (fish). Britannica Online Encyclopedia.
9. Francisco de Orellana (Spanish explorer and soldier). Britannica Online Encyclopedia.
10. Amazon Longer Than Nile River, Scientists Say
11. Tom Sterling: Der Amazonas. Time-Life Bücher 1979, 8th German Printing, p. 20
12. http://www.walkingtheamazon.com/

External links

• Amazon dries up Youtube (31 July 2006)
• Amazon Rainforest Fund
• Bibliography on Water Resources and International Law Peace Palace Library
• Information on the Amazon from Extreme Science
• Pictures of the Amazon River
• Information and a map of the Amazon's watershed
• Amazon Alive: Light & Shadow documentary film about the Amazon river
• http://www.extremescience.com/AmazonRiver.htm