The source of the Otra watercourse system is in Setesdalsheiene in Bykle municipality, Aust-Agder county. The Otra river then flows through Setesdalen and into the sea at Kristiansand. The system's catchment area is more than 3,700 square kilometres. The biggest lakes in the watercourse system are Åraksfjorden and Byglandsfjorden.

Around 2 per cent of Norway’s power production stems from the Otra watercourse system. Skagerak Kraft is part owner of Otrakraft, which owns and operates several of the large power plants in the watercourse. We are also a part owner of Hekni Power Plant.

There is salmon in the Otra river as far up as Vigeland in Vennesla, and a special type of salmon called Bleke salmon is found in the Byglandsfjord. The distinct calcium-rich soil in the uppermost part of Setesdal valley gives the river water a good buffer against acidification and provides favourable conditions for the salmon.

*The figures refer to plants where Skagerak Kraft holds an ownership interest.