The next time you want to impress your friends and influence your enemies with your knowledge of trivial and not-so-trivial facts, try the following on for size! The Amazon River is without competition the worlds greatest river. The Nile River of Africa is in competition for the title of Worlds Longest River (the winner being determined by how each river is measured), but for many reasons, the Amazon far surpasses the Nile and every other river in the world.

If size is important to you...
The average discharge of water into the Atlantic Ocean by the Amazon River is approximately 175,000 cubic meters per second, or between 1/5th and 1/6th of the total discharge into the oceans of all of the worlds rivers! This discharge is 4-5 times that of the Congo River, and 10 times that of the Mississippi River. The Rio Negro, a tributary of the Amazon, is the second largest river in the world in terms of water discharge, and is 100 meters (over 300 feet) deep and 14 kilometers (almost 9 miles) wide near its mouth at Manaus, Brazil.

Raindrops keep falling on my head!
Average rainfall across the whole Amazon basin is approximately 2300 mm (or 7.5 feet) annually. In some areas of the northwest portion of the Amazon basin, yearly rainfall can exceed 6000 mm (19.7 feet)!

Where does all that water go?
All of the water that is discharged into the Atlantic Ocean is actually only about 1/3rd of the water that falls into the Amazon basin as rain. Where does the other 2/3rds go? Up to half of the rainfall in some areas may never reach the ground, being intercepted by the forest and re-evaporated into the atmosphere. Additional evaporation occurs from ground and river surfaces, or is released into the atmosphere by evapo-transpiration from plant leaves. All of this evaporated moisture re-enters the water cycling system of the Amazon, and a given molecule of water may be "re-cycled" many times between the time that it is evaporated from the surface of the Atlantic Ocean and carried by the prevailing westerly winds into the Amazon basin, to the time that it is carried back to the ocean by the Amazon River.

A long and winding river road.
The total length of the Amazon River from its source springs in the Andes (taking the Ucayali River as the continuation of the main river into the Andes, and the short distance around Marajó Island at the mouth of the Amazon), is sometimes estimated at 6518 km (not including all river bends!), or 4075 miles in length. This is exceeded only by the Nile River (including the Kagera River) of Africa with a total length of 6671 km (4170 miles). However, if one measures the long way around Marajó Island, the lengths of the two rivers are virtually identical. Additionally, a recent National Geographic expedition is reported to have found the most-distant spring of the Amazon - exact "new" length of the Amazon is yet to be determined! The headwaters of the Amazon are located high in the Andes at an elevation of about 5,200 meters (17,000 feet), and only 190 kilometers (120 miles) from the Pacific Ocean.

Like mothers, like daughters...
Two of the tributaries of the Amazon, the Juruá and the Madeira Rivers, are both over 3,300 km (2,060 miles) long. About 1,100 other tributaries empty into the Amazon River.

Momma was not a Rolling Stone!
After leaving the Andes, the elevational gradient of the Amazon is very low. At Iquitos, Peru, still some 3,600 km (2,250 miles) from the Atlantic, the river-level at low-water season is only about 100 m (a bit more than 300') above sea-level, and the slope is around 2 cm (less than one inch) vertical change per kilometer. In the lower Amazon, at the mouth of Rio Negro and still 1,500 km from the Atlantic, the river-level at low-water season is only 15 m above sea-level, and the slope is about 1 cm per kilometer.

Talk about a big mouth!!
The mouth of the Amazon is over 320 km wide (approximately 200 miles), and contains the worlds largest freshwater island, Marajó Island, with an area of 48,000 km2.

NEWS FLASH!! Rumpelstiltskin Drowns in Slow Flood.
The Amazon is not a good place to fall permanently asleep on the river bank! Seasonal water levels can vary up to 20 meters (65 feet) in the middle Amazon region. Towards the mouth of the Amazon, the yearly change becomes less and less, but even near the mouth of the Amazon (at the Rio Xingu), it is still 4 meters (12 feet).

Flooded but not drowned.
The seasonal variation in water levels means that huge areas along the major rivers in the Amazon basin are periodically flooded. The total area of flooded, or varzea, forest is between 50-60,000 km2, or about 4% of the total forest area. These flooded forest areas may extend as much as 80 kilometers (50 miles) from the main river channels, and the forest vegetation of the varzea is well adapted to being seasonally flooded. The structure and species composition of the varzea is very different from non-flooded upland (or terra firme) forest areas. Varzea forest areas are critical to the freshwater fisheries of the Amazon Basin.

Go with the flow.
Despite the low slope of the Amazon, the river currents can be surprisingly strong. In the lower Amazon (with the lowest slope), current speeds range from 0.5-1.0 meters per second at low water, and twice that at flood stage. In localized areas, current speeds can reach as high as 3 meters (9.8 feet) per second.

Ships on a submarine river??
The width of the Amazon at Iquitos, Peru (3,600 km/2,250 miles from the ocean) is about 2 km. Ocean-going ships can easily access the Port of Iquitos at high water, as the mean depth of the current-canal of the Amazon is between 40 and 50 m (or up to 150+ feet deep), and in places, over 100 m (over 300 feet) deep. Even hundreds of miles away from the ocean, sections of the bottom of the river channel actually lie below sea level!

World's Biggest Outhouse!
In the Atlantic Ocean beyond the mouth of the Amazon, and resting on the continental shelf, the Amazon sediment cone has a length of about 680 km and a width of 250 km. These fine grained deposits (mostly clay/mud particles) on the ocean floor are over 11,000 meters (36,000 feet) thick. This is mostly sediment that has been carried down river from the Andes Mountains, the Guianan Shield (to the North) and the Brazilian Shield (to the south), by the river current, and which settled out of the water column once the river current dissipated into the waters of the Atlantic Ocean.

World's Biggest Washtub.
The Amazon basin (the watershed of the Amazon River) is 7,050,000 km2 in area (or about 2,500,000 square miles), and covers about 40% of South America. Of this area, approximately 5,000,000 km2 is (or was) covered by high tropical rainforest, with the remainder covered by savannah ("campo") or scrubby woodland ("cerrado"). The Amazon basin covers significant portions of the countries of Brazil, Peru, Colombia, Ecuador, Venezuela and Bolivia, though the major part of the watershed lies within Brazil. The next largest tropical watershed, that of the Congo River, at 3,690,000 km2, is only half the size of the Amazon basin.

A Bouillabaisse of Fishes.
The Amazon basin is home to over 2,400 known species of fish, more species than are found in the entire Atlantic Ocean! Some scientists estimate that there may be as many as 5,000 species! These range from giant air-breathing fish (Arapaima gigas) and river catfish weighing up to 600-700 lbs, to tiny tetras, electric eels, sting-rays, needlefish, fresh-water flying-fish, and knife-fish. The fish fauna of many river systems is poorly known, and new species are discovered yearly, even in the "better-known" areas!

Violent Revolution Rocks South America!
Although it now empties into the Atlantic Ocean, the Amazon once flowed into the Pacific! The uplift of the Andes Mountains about 65 million years ago in a geological event called the Laramide Revolution cut the flow to the Pacific, and forced the Amazon River to flow eastward. This revolution took place when the westward-moving South American (geological or tectonic) plate crashed headlong into the eastern-moving Nazca Plate. The Nazca plate was forced beneath the South American plate, lifting up the Andes mountains in a process that continues to this day, as evidenced by the many earthquakes and high volcanic activity of the Andes region.

But It's a Dry Heat...
The Amazon basin has not always been an area of lush tropical rainforest. At several times during its history, the basin has been the location of huge lakes and shallow seas. Salt deposits up to 600 meters thick (nearly 2000 feet!) have also been found in some locations, indicating that at one time, the basin may have been desert-like, drying up the shallow seas and creating the salt deposits.

A Well Watered Desert!
Would you believe that the Amazon has its own sand dunes? Echogrammes of the river bed below the mouth of the Rio Negro show giant sand dunes as long as 600 meters (2000 feet) and up to 12 meters (39 feet) in height. These dunes are gradually moved downstream in the same manner that wind moves sand-dunes in "true" deserts!

SOURCES
Many of the above Amaz(on)ing Facts are adapted from the following sources:

The Amazon. Limnology and Landscape Ecology of a Mighty Tropical River and its Basin. (1984) H. Sioli, editor. Dr. W. Junk Publishers, Dordrecht (ISBN 90-6193-108-8).
A compilation of contributions of various experts on the Amazon, and packed full of information. While some of it is somewhat technical, most of the information is readily accessible by an interested layperson. The most difficult part is likely to be finding a copy - a university library (or very large city library) is probably your best bet.

A Neotropical Companion, 2nd Ed. (1997) J. C. Kricher. Princeton Univ. Press, Princeton, New Jersey, 451 pages. (ISBN 0-691-04433-3).
An excellent, all-round introduction to the natural history of the American humid tropics. The second edition is a considerable improvement over the first, with more comprehensive coverage of the Amazon Basin. The treatment of many topics is necessarily superficial, but many references are included for additional detail. An excellent starting point for learning about and/or visiting the tropical forests of the Americas.