Although not technically wrong, a heated debate surrounds the title of the world's longest river. Most of us probably learned in school that the river Nile is the world's longest. However, an expedition in 2007 traced the Amazon river's source to mountains in southern Peru, thus extending its length to 4,345 miles (6,992km). Although, because of the Amazon's complex and variable streambed, affected by seasonal factors, an accurate measure is complicated to get and the total length remains open to interpretation.