While the Amazon is clearly the largest river in the world by most measures, the majority of the geographic community today regards the Amazon as the second longest river, just slightly shorter than the Nile. However the discovery of a new tributary of the Amazon now leads some scientists to consider the Amazon as the longest river in the world.
The area covered by the water of the River and its tributaries more than triples over the course of a year. In an average dry season 110,000 square kilometres (42,000 sq mi) of land are water-covered, while in the wet season the flooded area of the Amazon Basin rises to 350,000 square kilometres (135,000 sq mi). At its widest point the Amazon River can be 11 kilometres (7 mi) wide during the dry season, but during the rainy season when the Amazon floods the surrounding plains it can be up to 45 kilometres (28 mi) wide.
The quantity of water released by the Amazon to the Atlantic Ocean is enormous: up to 300,000 m³ per second in the rainy season. The Amazon is responsible for a fifth of the total volume of fresh water 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 two hundred kilometres out to sea.
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 pongos, the Marañón River flows about 1,600 kilometres (1,000 mi) 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 5,597 m (18,363 ft) peak called Nevado Mismi in the Peruvian Andes, roughly 160 km (100 mi) west of Lake Titicaca and 700 km (430 mi) 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.
Formally, though, the union of the Ucayali and the Marañón form the Amazon River, which changes its name to Solimões on the triple frontier between Peru, Colombia and Brazil, and later changes its name back to the Amazon only after it meets the Rio Negro near Manaus. This confluence is known in Brazil as the "Meeting of Waters" (Portuguese: Encontro das Águas) as the dark almost black colored waters of the Rio Negro meet the sandy colored Rio Solimões, and for over 6 km these waters run side by side without mixing. Solimões is only known by Brazilians, because for Peruvians and Colombians the name is always Amazon River.
After the confluence of Río Apurímac and Ucayali, the river leaves Andean terrain and is instead surrounded by flood plain. From this point to the Marañón, some 1,600 km (990 mi), 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 average depth of the river in the height of the rainy season is 40 m (131 ft) and the average width can be nearly 40 km (25 mi). It starts to rise in November, and increases in volume until June, then falls until the end of October. The rise of the Negro branch is not synchronous; the rainy season does not commence in its valley until February or March. By June it is full, and then it begins to fall with the Amazon. The Madeira rises and falls two months earlier than the Amazon.
The main river (which is between approximately one and six miles (10 km) wide) is navigable for large ocean steamers to Manaus, 1,500 kilometres (930 mi) upriver from the mouth. Smaller ocean vessels of 3,000 tons and 5.5 metres (18 ft) draft can reach as far as Iquitos, Peru, 3,600 kilometres (2,240 mi) from the sea. Smaller riverboats can reach 780 kilometres (485 mi) higher as far as Achual Point. Beyond that, small boats frequently ascend to the Pongo de Manseriche, just above Achual Point.
The breadth of the Amazon in some places is as much as 6 to 10 kilometres from one bank to the other. 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 5 metres (16 ft) above low river, into many islands.
From the village 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 17 m (56 ft) 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 240 kilometres (149 mi) from opposite the mouth of the Xingu as far as Monte Alegre. These hills are cut down to a kind of terrace which lies between them and the river.
Monte Alegre reaches an altitude of several hundred meters. On the south bank, above the Xingu, an almost-unbroken line of low bluffs bordering the flood-plain extends nearly to Santarem, in a series of gentle curves before they bend to the south-west, and, abutting upon the lower Tapajos, merge into the bluffs which form the terrace margin of the Tapajos river valley.
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 (2,100,000 sq mi) and is among the richest tropical forests in the world. Amazon river has over 3,000 recognized species of fish and that number is still growing. Some estimates go as high as 5,000.
The waters of the Amazon support a diverse range of wildlife. Along with the Orinoco, the river is one of the main habitats of the Boto, also known as the Amazon River Dolphin. The largest species of river dolphin, it can grow to lengths of up to 2.6 metres (9 ft). The boto is the subject of a very famous legend in Brazil, about a dolphin that turns into a human.
Also present in large numbers are the notorious Piranha, carnivorous fish which congregate in large schools, and may attack livestock and even humans. Although many experts believe their reputation for ferocity is unwarranted, a school of piranha was apparently responsible for the deaths of up to 300 people when their boat capsized near Óbidos in 1981. However, only a few species attack humans, and many are solely fish-eaters, and do not school.
The bull shark (Carcharhinus leucas) has been reported 4,000 km (2,220 miles) up the Amazon River at Iquitos in Peru. The arapaima, or 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 3 m (9.8 ft) and weight up to 200 kg (440 lb). Another amazonian freshwater fish is the arowana (Osteoglossum bicirrhosum) which is also a predator and very alike the arapaima, but reaches a length of maximum 120 centimetres.
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. Anacondas have been known to occasionally attack fishermen .
The river supports thousands of species of fish, as well as crabs, algae, turtles, and chicken.
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 attacked by fierce female warriors like the mythological Amazons. The icamiabas Indians dominated the area closed to the Amazon river, rich in gold. When Orellana went down the river in search of gold, descends Andes (in 1541), the river was still called Grande Rio, Mar Dulce or Rio da Canela (Cinnamon), because of the great trees of cinnamon located there. The belligerent victory of the icamiabas against the Spanish invaders was such that the fact was narrated to the king Carlos V, whom, inspired by the Greek amazons, baptized the river as Amazon.
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 putatively savage indigenous peoples of the vast rain forest.
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. In Brazil, the principal commercial city, Para (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 from 1,000 to 1,500 population. All the remaining villages, as far up as Tabatinga, on the Brazilian frontier of Peru, were relatively small.
On 6 September 1850, the emperor, Peter II, sanctioned a law authorizing steam navigation on the Amazon, and gave the Baron of Mauá (Irineu Evangilista de Sousa) the task of putting it into effect. He organized the "Compania de Navigacao e Commercio do Amazonas" at 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 Para and Cameta. 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; Cameta—on the Tocantins; Santarem—on the Tapajos; Borba—on the Madeira and Manáos—on the Rio Negro. The Brazilian decree took effect on 7 September 1867.
Thanks in part to the mercantile development associated with steam boat navigation, coupled with the internationally driven demand for natural rubber (1880-1920), Manáos (now Manaus), Para (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 boom-town was known abroad as the St. Louis of the Amazon.
The first direct foreign trade with Manáos 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, Purfis 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 pelts and exotic forest produce (resins, barks, woven hammocks, prized bird feathers, live animals, etc.) and extracted goods (lumber, gold, etc.).
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, the demand for rubber from the Allied forces in World War II providing funding for the drive.
The construction of the new capital Brasilia in the interior in 1960 also contributed to the opening up of the Amazon basin. A large scale colonization program saw families from north-eastern 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 Trans-Amazon highway network began. The network's three pioneering highways were completed within ten years, connecting all the major cities of the Brazilian Amazon interior.
A study by Brazilian scientists claimed that the Amazon is actually longer than the Nile. Using Nevado Mismi, which was labelled by the National Geographic Society as the Amazon's source back in 2001, 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.
Moreover, in 2008, the Peruvian institution of La Sociedad Geográfica de Lima conducted a joint research with the international scientific community to locate the source of the Amazon. After extensive research, they officially proved that the Andes in southern Peru were the source of the Amazon. Among the list of scientific institutions that agree with these findings are the Geographic Society of London, the Russian Academy of Science, and the Brazilian Institute of Space Research.
The Amazon has over 1,000 tributaries in total, 17 of which are over 1,000 kilometers. Some of the more notable: