Is the largest river in the world by volume, with a total river flow greater than the next top ten largest rivers flowing into the ocean combined.
The Amazon, which has the largest drainage basin in the world, accounts for approximately one fifth of the world's total river flow. Because of its vast dimensions, it is sometimes called The River Sea. At no point is the Amazon crossed by bridges. This is only partly because of its huge dimensions in fact, for most of its length the Amazon is not so wide that a modern bridge could not span it but more because, for most of its length, the river flows through tropical rainforest, where there are few roads and even fewer cities.
While the Amazon is clearly 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.
The Amazon basin, the largest drainage basin in the world, covers some 40 percent of South America, an area of approximately 6,915,000 square kilometers (2,670,000 sq mi). 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 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 five hundred kilometers 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 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.
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 Amazon River runs mostly through Brazil and Peru. The countries it branches off into consist of Venezuela, Colombia, Ecuador, and Bolivia.
