The Amazon River or River Amazon (Portuguese: Rio Amazonas; Spanish: Río Amazonas) of South America is the largest river in the world by volume, with greater total river flow than the next eight largest rivers combined, and with the largest drainage basin in the world. Because of its vast dimensions it is sometimes called The River Sea (o rio-mar in Portuguese). Debate as to whether the Amazon or the Nile is the world's longest river has gone on for many years, with the consensus during the 20th century being that, by possibly only a few kilometers, the Nile is the longer of the two (see below)
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 mi²) 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 mi²).citation needed] 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 fresh 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 a hundred miles out to sea. In 1500, Vicente Yañez Pinzón was the first European to sail into the river. Pinzón called the river flow "río Santa María de la Mar Dulce", finally the name was shortened to "Mar Dulce" (sweet sea).
The Amazon estuary is over 325 kilometres (202 mi) wide. The main river (which is between approximately one and six miles 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 Amazon drains an area of some 6,915,000 square kilometres (2,670,000 mi²), or some 40 percent of South America. 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 Amazon has changed its course several times. In early Cenozoic times, before the uplifting of the Andes, it flowed westward.
The Upper Amazon has a series of major river systems in Peru (many of which are alike in Ecuador) that flow North and South into the Marañón and Amazon River. Among others, these include the following rivers: Morona, Pastaza, Nucuray, Urituyacu, Chambira, Tigre, Nanay, Napo, Huallaga, and Ucayali. All of these are longer than any river in Europe. The same as in the snow-crested Andes high above Lake Lauricocha in central Peru, the headstream of the Marañón River rises in 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 1,000 miles (1,600 km) from west-central to northeast Peru before it combines with the Ucayali River, just below the provincial town of Nauta, to form the mighty Amazon River. The primary tributaries of the Marañón River are--from south to north--the Crisnejas, Chamayo, Urtcubamba, Cenepa, Santiago, Moroña, Pastaza, Huallaga, and Tiger Rivers (Cavero-Egusquiza 1941:49-51).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 Río Amazonas, 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.
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.