World rivers

http://www.woodlands-junior.kent.sch.uk/Homework/rivers/longest.htm

http://www.factmonster.com/ipka/A0001779.html

http://www.rev.net/~aloe/river/

http://en.wikipedia.org/wiki/List_of_rivers_by_length

http://mx.kalipedia.com/geografia-general/tema/graficos-principales-rios-mundo.html?x1=20070417klpgeogra_24.Ees&x=20070417klpgeogra_17.Kes