Langvassåga is a river that flows out of the lake Langvatnet in the municipality of Rana in Nordland county, Norway. It flows in a southeastern direction and almost immediately, it is joined by the river Røvassåga. It then continues a short distance southwards before joining the main river Ranelva, just south of the village of Røssvoll. The Langvassåga catchment area covers about 1,114 square kilometres (430 sq mi). The river passes by the Mo i Rana Airport, Røssvoll.

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  Bridge on E6 above Langvassåga just before it meets Ranelva
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  Langvassåga west of the bridge
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  Langvassåga meets Ranelva east of the bridge

• List of rivers in Norway