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Rivers are defined as natural flowing freshwater bodies that move from a high elevation to a lower elevation, finally draining into oceans, lakes, seas, or other rivers. It is challenging to precisely determine the world's longest river from so many long rivers located throughout the different continents of the planet.
Although most of us believe that the Nile River is the longest, some scholars have claimed that the Amazon River is the longest of all rivers. In 2009, a peer-reviewed article published in the "International Journal of Digital Earth" cleared the confusion and declared the Nile River - the longest river in the world.
This is a list of the longest rivers on Earth. It includes river systems over 1,000 kilometers (620 mi).
Details at USGS