Amazon vs. Nile

For now, Amazon leading by a source tributary.

Quick excerpt:
Geographers long agreed that, while the Amazon might be the world’s largest river by volume, the longest was likely the Nile. In 2007, however, the BBC reported that a team of Brazilian researchers challenged that long-held belief. After an expedition to Peru to locate the Amazon’s precise source, the team described a different starting point. The team claimed that the river originated not in northern Peru, where it had been thought to begin, but in southern Peru, somewhere on snowcapped Mount Mismi (or Nevado Mismi). The team narrowed down the starting point to one of two places, but concluded that either one would nudge the Amazon’s length past that of the Nile.

Full story:
http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17693