Amazon River
Dispute regarding length

While debate as to whether the Amazon or the Nile is the world's longest river has gone on for many years, the historic consensus of geographic authorities has been to regard the Amazon as the second longest river in the world, with the Nile being the longest. However, the Amazon has been reported as being anywhere between 6,275 km (3,899 mi) and 6,992 km (4,345 mi) long. It is often said to be "at least" 6,575 km (4,086 mi) long. The Nile is reported to be anywhere from 5,499 to 7,088 km (3,417 to 4,404 mi). Often it is said to be "about" 6,650 km (4,130 mi) long. There are several factors that can affect these measurements, such as the position of the geographical source and the mouth, the scale of measurement, and the length measuring techniques (for details see also List of rivers by length).

In July 2008, the Brazilian Institute for Space Research (INPE) published a news article on their webpage, claiming that the Amazon River was 140 km (87 mi) longer than the Nile. The Amazon's length was calculated as 6,992 km (4,345 mi), taking the Apacheta Creek as its source. Using the same techniques, the length of the Nile was calculated as 6,853 km (4,258 mi), which is longer than previous estimates but still shorter than the Amazon. The results were reached 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. According to an earlier article on the webpage of the National Geographic, the Amazon's length was calculated as 6,800 km (4,200 mi) by a Brazilian scientist. In June 2007, Guido Gelli, director of science at the Brazilian Institute of Geography and Statistics (IBGE), told London's Telegraph Newspaper that it could be considered that the Amazon was the longest river in the world. However, according to the above sources, none of the two results was published, and questions were raised about the researchers' methodology. In 2009, a peer-reviewed article, was published, concluding that the Nile is longer than the Amazon by stating a length of 7,088 km (4,404 mi) for the Nile and 6,575 km (4,086 mi) for the Amazon, measured by using a combination of satellite image analysis and field investigations to the source regions. According to the Encyclopædia Britannica, the final length of the Amazon remains open to interpretation and continued debate.
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