The Ounasjoki[1] (Northern Sami: Ovnnesjohka) is the Kemijoki's largest tributary and is Finland's longest single river tributary. It is also the largest river entirely within its borders. Ounasjoki is approximately 299.6 kilometres (186.2 mi) in length, and the catchment area is 13,968 square kilometres (5,393 sq mi), 27% of the Kemijoki catchment area.
Course
The Ounasjoki originates at Ounasjärvi lake in Enontekiö. It flows first eastwards through Periläjärvi lake and turns south after some seven kilometres. The river then follows southern-southeasterly course until its confluence with the Kemijoki at Rovaniemi.
