Amazon -- Rio Negro & Amazon River
Today the Amazon River is the most voluminous river on Earth, eleven times the volume of the Mississippi, and drains an area equivalent in size to the United States. During the high water season, the river's mouth may be 300 miles wide and every day up to 500 billion cubic feet of water (5,787,037 cubic feet/sec) flow into the Atlantic. For reference, the Amazon's daily freshwater discharge into the Atlantic is enough to supply New York City's freshwater needs for nine years. The force of the current -- from sheer water volume alone -- causes Amazon River water to continue flowing 125 miles out to sea before mixing with Atlantic salt water. Early sailors could drink freshwater out of the ocean before sighting the South American continent.
The river current carries tons of suspended sediment all the way from the Andes and gives the river a characteristic muddy whitewater appearance. It is calculated that 106 million cubic feet of suspended sediment are swept into the ocean each day. The result from the silt deposited at the mouth of the Amazon is Majaro island, a river island about the size of Switzerland.
The best known blackwater river is one of the world's largest rivers (5 miles at its mouth), the Rio Negro in Brazil. In contrast to the white water Amazon (the Rio Solimones at this point) which has its origins in the mountain valleys of the Andes, the tributaries of the Rio Negro rise in the ancient rock formations of the Guyana shield and flow through white sands rainforests. The differences between the blackwater of the Rio Negro and the whitewater Amazon are readily apparent where two rivers meet near Manaus, Brazil. The rivers run side by side, clearly distinct as separate white and black water, before blending together after several miles.
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The Amazon River (occasionally River Amazon; Spanish: Río Amazonas, Portuguese: Rio Amazonas) of South America is one of the longest two rivers on Earth, the Nile River in Africa being the other. The Amazon has by far the greatest total flow of any river, carrying more than the Mississippi, Nile, and Yangtze rivers combined. It also has the largest drainage area of any river system. It may be correctly stated that the Nile is the longest river, while the Amazon is the strongest.
The quantity of fresh water released to the Atlantic Ocean is enormous: 184,000 m³ per second (6.5 million ft³/s) in the rainy season. Indeed, the Amazon is responsible for a fifth of the total volume of fresh water entering the oceans worldwide. It is said that 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.
The main river (which is usually between one and six miles wide) is navigable for large ocean steamers to Manaus. Smaller ocean vessels of 3,000 tons and 5.5 m (18 ft) draft can reach as far as Iquitos, 3,700 km (2,300 miles) from the sea. Smaller riverboats can reach 780 km (486 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 6,915,000km² (2,722,000 mile²), 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; and, after a course of about 7,200 km (4,800 mi) through the interior of Peru and across Brazil, it enters the Atlantic Ocean at the equator.