Which river is Norway's longest and most voluminous?

The Glomma is Norway’s longest and most voluminous river. Also called Glåma in parts of Norway, it runs for about 621 kilometres through the country’s southern interior before reaching the Skagerrak.

The river rises at Lake Aursunden near Røros in Trøndelag and flows south through the forested Østerdalen valley. Its largest tributary is the Vorma, which carries water from Lake Mjøsa. At Fetsund, the Glomma enters Lake Øyeren and forms Europe’s largest inland delta, an area built from sediment carried downstream.

Forests made the Glomma central to Norway’s historic timber industry: logs were floated along it, and waterpower encouraged mills, factories and other industry. Its lower course reaches the sea at Fredrikstad, where transport, ports and hydropower helped support settlement. The Tana is another notable Norwegian river, but at roughly 361 kilometres it is far shorter; Otra and Numedalslågen are shorter as well.