Numedalslågen stretches for over 250 kilometres (160 mi) through the counties of Vestfold and Telemark and Viken_(county), beginning at the Hardangervidda plateau and meeting the ocean at Larvik in Vestfold. Numedalslågen is one of Norway's longest rivers. The river runs through the municipalities Larvik, Lardal, Kongsberg, Flesberg, Rollag and Nore og Uvdal.