Amazon River - ‘The River Sea’

From its humble beginnings high in the Peruvian Andes, within 100 miles [160 km] of the Pacific Ocean, the Amazon—swollen by the waters of other rivers along its way—descends some 16,000 feet [5,000 m] to the Atlantic Ocean. It changes name several times before reaching Brazilian territory, where it is first called the Solimões. After its confluence with its most voluminous tributary, the Negro River, near Manaus, it becomes the mighty Amazon.

At this point an unusually beautiful spectacle called the meeting of the waters occurs. The dark coffee-colored waters of the Negro River and the muddy waters of the Solimões meet and flow side by side without mixing for approximately six miles [10 km]. This phenomenon occurs as a result of various factors, including the difference in composition, density, and temperature between the two rivers.

The controversy that surrounds the Amazon’s main tributaries and their headwaters, as well as the complicated geography of its delta, makes it difficult to know exactly where the Amazon begins and where it ends. Based on its most distant outlet in the Pará estuary, which serves as an entry point for shipping, its length is approximately 4,200 miles [6,750 km]. Determining its total length, though, is “more a question of definition than a question of measurement,” says the Brazilian edition of The Guinness Book of Records.

In volume, however, the majesty of the Amazon River is undisputed. Its volume is greater than that of the Mississippi, Nile, and Yangtze rivers combined. With an average discharge of over 7,000,000 cubic feet [200,000 cu m] per second, this monumental river empties into the Atlantic Ocean between 15 and 20 percent of all the fresh water that flows into the world’s oceans. In just 30 seconds, it could quench humanity’s thirst for a day—two pints [one liter] of water for each of earth’s six billion inhabitants!

This extraordinary outpouring “pushes” the sea and forms a layer of fresh water spreading 125 miles [200 km] out into the Atlantic Ocean. It is not surprising that on sighting the river’s mouth, Vicente Yáñez Pinzón, a Spanish navigator who entered the Amazon in June 1500, called it Mar Dulce (the Freshwater Sea).

For those who travel on this great river, it seems to be just that—a sea flooding a carpet of forests. At some points it is so broad that a person on one of its banks cannot see the other side. During floods certain stretches of the river are up to 30 miles [50 km] wide! Its depth, averaging from 150 to 250 feet [50 to 80 m] at some stretches, varies according to its width. At its narrowest point, at Óbidos in Pará State, the river is 420 feet [130 m] deep.

Most of the Amazon has a very slight slope—averaging a mere one and a quarter inches per mile. The gentle slope of its estuary allows the tide to penetrate far upstream. Its effects are felt even at Óbidos, 500 miles [800 km] from the river’s mouth.

Because it flows almost parallel to the equator, the Amazon benefits from the summers of both hemispheres. Flooding alternates between the tributaries on the left bank and those on the right bank. As the levels of the rivers rise and fall, first on the north side and then on the south side, the entire Amazon pulsates like a huge heart. Annually, the oscillation of the Amazon’s water level varies between 30 and 40 feet [9 and 12 m]. Flooding is important for agriculture in the region. Because a considerable quantity of mineral substances and organic residues are carried by the river and deposited on its banks, it fertilizes the large lowland areas.