Lesjaskogsvatnet

The lake is unusual by having two outlets, one in each end: It flows both East into the Gudbrandsdalslågen and west into the Rauma river in the Romsdalen valley. The lake serves as the headwaters for two major rivers: Gudbrandsdalslågen and for Rauma River . Gudbrandsdalslågen flows through the Gudbrandsdalen valley floor, ending in lake Mjøsa. The lake sits on the watershed in the north-western corner of Glomma drainage system that includes large parts of eastern Norway.
The lake was dammed to serve the Lesja Iron Works in the 1660s. The east end was lifted 3 meters, the west end was lifted by a small stone wall. Earlier the lake was shorter and concentrated in what is now the west end of the lake. About 67% of the water flows to Rauma, at low water level about 80% flows to Rauma. Rotting plants and fish on the bottom produces gas that in winter is captured under the ice. The watershed has over thousands of years shifted east because rivers and glaciers to west dig more into the bedrock, notably in the upper part of Rauma river near Verma village.

Wikipedia