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].a 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.b 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!

The Amazon basin is the largest river basin in the world, covering some two million square miles [6 million sq km]. It is larger than the whole of Europe excluding Russia. Along with its 1,100 tributaries and other smaller watercourses, the Amazon forms a complex communications network that could be likened to the circulatory system of the human body, of which the Amazon compares to the aorta, the body’s largest artery. This network of waterways contains two thirds of all the earth’s fresh water. This extensive hydrographic network, with over 15,000 miles [25,000 km] of navigable waters, plays a fundamental role in transportation and in the lives of the local people.

Millions who dwell in the Amazon region use this natural superwaterway. Boats of all sizes sail along it, including large transatlantic vessels that travel 1,000 miles [1,500 km] upstream to Manaus. Lesser freight and passenger vessels reach as far as Iquitos, in Peru, 2,300 miles [3,700 km] from the mouth of the river.