Wikipedia
Hallingdalselva is a river which flows through the valley and traditional district of Hallingdal in Buskerud County, Norway. In the valley, the river is often referred to as Storåne ("the great river").
The 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.
A number of rivers flow into the Hallingdal River including the Votna, Lya, Hemsil, Todøla and Rukkedøla. Hallingdal River has a total length of and a catchment area of . The river falls in its journey to Krøderen, which is above sea-level. There are many hydro-electric power stations in the valley with an annual power production of about 4 TWh. The whole river system is now almost fully developed with a total of 13 power plants. The largest plants are Hol I-III (275 MW), Nes (250 MW), Usta (184 MW) and Hemsil I-II (152 MW). The total average annual production is approximately 4143 GWh. Most of the waterfall rights are owned by E-CO Energi.