Dalälven (dälˈĕlˌvən) [key], river, c.325 mi (520 km) long, Kopparberg co., W central Sweden, in the mountains along the Norwegian border. It flows SE to Avesta, then NE into the Gulf of Bothnia at Skutskar. The Västerdalälven is its chief tributary. The river passes through the Siljan agricultural region and the Bergslagen and Domnarvet iron-mining districts. Numerous cascades furnish power for industries.