Fossen () is a waterfall along the SjønstÃÂ¥ River in Fauske Municipality in Nordland county, Norway. It is about upriver from the SjønstÃÂ¥ farm.
In 1892, the Sulitjelma Line was built between SjønstÃÂ¥ and Fossen, replacing an unimproved road from 1888. Ore from Sulitjelma Mines was transported by boat across the lake Langvatnet (Long Lake) from Sulitjelma to Fossen, and then by rail from Fossen to SjønstÃÂ¥ to be taken by boat via the lake ÃÂvervatnet (Upper Lake) and Nervatnet (Lower Lake), so that it could be sent by ship from Finneid along Skjerstad Fjord. The line was extended from Fossen to Hellarmo a year later.
The Sulitjelma Line was discontinued on July 23, 1972 and the station at Fossen is no longer used.