When it comes to length, the Amazon River has always ranked No. 2 - slightly shorter than Africa's Nile, slightly longer than China's Yangtze.
Now scientists - not surprisingly from Brazil - say it's time to change the score.
According to that nation's Institute of Geography and Statistics, researchers have long known that the real source of the Amazon was not where people thought it was.
An expedition in 2000, followed by another this year, traced the Amazon's headwaters beyond their long-accepted source, the Marañón River. Aided by satellite navigation, explorers continued south, to a trickle in the Peruvian Andes.