Glåma or Glomma (both: glôˈmä) [key], longest river of Norway, c.365 mi (590 km) long, rising in the highlands of Sør-Trøndelag co., SE Norway. It flows generally S past Sarpsborg (the head of navigation), into the Skagerrak at Fredrikstad. The Vorma River, which drains Mjøsa Lake, is its chief tributary. The Glåma's numerous waterfalls are the sites of hydroelectric stations; the lower river furnishes power to the urban industrial complex between Sarpsborg and Fredrikstad. The Glåma, passing through a heavily forested region, is Norway's chief timber-floating river.