The Gudbrandsdalslågen (or simply Lågen) is a river which flows through the Gudbrandsdal valley in Innlandet county, Norway.

The river flows through the municipalities of Lesja, Dovre, Sel, Nord-Fron, Sør-Fron, Ringebu, Øyer, and Lillehammer.

[1] The Gudbrandsdalslågen begins in the lake Lesjaskogsvatnet (or Lesjavatn), which lies in Lesja municipality in the far northern part of the county.

The eastern rivers, Jora, Ula, Frya, Tromsa, and Mesna are shorter and drop precipitously from the heights of the Rondane mountains.

Although relatively placid for extended stretches of its 204-kilometre (127 mi) path, the Gudbrandsdalslågen drops rapidly through the Rosten Gorge in Sel Municipality.

[8] The Hunder trout is bred at the Hunderfossen waterfall on the Gudbrandsdalslågen river, by the 280-metre (920 ft) long power station dam.

There is a hatchery on the west bank; it produces 20,000 hunder trout every year and releases them into the river to compensate for the loss of fish and of spawning grounds when the power plant was established.