Hallingdal River rises from within the Hardangervidda mountain plateau. Hallingdal River is formed by the confluence of the Usta River which flows from Lake Ustevatn and the Holselva River from Lake Strandavatnet. Hallingdal River flows from the north into Lake Krøderen (Krøderfjorden) at Gulsvik. Lake Krøderen discharges via the Snarumselva (Snamum river) at the south end of the lake.