<P> A study by Brazilian scientists concluded that the Amazon is actually longer than the Nile . Using Nevado Mismi, which in 2001 was labelled by the National Geographic Society as the Amazon's source, these scientists made new calculations of the Amazon's length . They calculated the Amazon's length as 6,992 kilometres (4,345 mi). Using the same techniques, they calculated the length of the Nile as 6,853 kilometres (4,258 mi), which is longer than previous estimates but still shorter than the Amazon . They made it possible by measuring the Amazon downstream to the beginning of the tidal estuary of Canal do Sul and then, after a sharp turn back, following tidal canals surrounding the isle of Marajó and finally including the marine waters of the Río Pará bay in its entire length . Guido Gelli, director of science at the Brazilian Institute of Geography and Statistics (IBGE), told the Brazilian TV network Globo in June 2007 that it could be considered as a fact that the Amazon was the longest river in the world . However, other geographers have had access to the same data since 2001, and a consensus has yet to emerge to support the claims of these Brazilian scientists . The length of both the Amazon and the Nile remains open to interpretation and continued debate . </P> <P> The Amazon basin, the largest in the world, covers about 40% of South America, an area of approximately 7,050,000 square kilometres (2,722,020 sq mi). It drains from west to east, from Iquitos in Peru, across Brazil to the Atlantic . 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 . </P> <P> The Amazon River and its tributaries are characterised by extensive forested areas that become flooded every rainy season . Every year, the river rises more than 9 metres (30 ft), flooding the surrounding forests, known as várzea ("flooded forests"). The Amazon's flooded forests are the most extensive example of this habitat type in the world . In an average dry season, 110,000 square kilometres (42,000 sq mi) of land are water - covered, while in the wet season, the flooded area of the Amazon basin rises to 350,000 square kilometres (140,000 sq mi). </P> <P> The quantity of water released by the Amazon to the Atlantic Ocean is enormous: up to 300,000 cubic metres per second (11,000,000 cu ft / s) in the rainy season, with an average of 209,000 cubic metres per second (7,400,000 cu ft / s) from 1973 to 1990 . The Amazon is responsible for about 20% of the Earth's fresh water entering the ocean . The river pushes a vast plume of fresh water into the ocean . The plume is about 400 kilometres (250 mi) long and between 100 and 200 kilometres (62 and 124 mi) wide . The fresh water, being lighter, flows on top of the seawater, diluting the salinity and altering the colour of the ocean surface over an area up to 2,500,000 km (970,000 sq mi) in extent . For centuries ships have reported fresh water near the Amazon's mouth yet well out of sight of land in what otherwise seemed to be the open ocean . </P>

When did the amazon become the longest river