The river Numedalslågen is Norway´s second longest river. From the western part of Hardangervidda (the highest mountain plateau in Europe) the river runs through the Numedalen valley to the town of Larvik.
The lower part of the valley is called Lågendalen. In the upper regions there are a number of hydroelectric power plants. Downstream from Hvittingfoss, however, the river runs wild, constantly changing from quiet parts to rapids and waterfalls, through the natural and cultural landscape. This is the salmon-bearing stretch of the river.