The Begna is a river in Buskerud and Oppland counties in Norway. It is formed by the merging of the rivers Otrøelva and Ylja above Lake Vangsmjøsa. It is also the name of the village of Begna located by the river. The Norwegian writer, Mikkjel Fønhus lived much of his life and located most of his novels along the Begna in Oppland. 
The Begna runs from the mountainous area of Filefjell in the southern part of the Jotunheimen range, through the traditional district of Valdres into the lakes Vangsmjøsi, Slidrefjord, Strondafjorden and Aurdalsfjorden, down Begnadalen to Nes in Ådal and Lake Sperillen via the Ådal River and southward to the city of Hønefoss in Buskerud. At Hønefoss, the Begna cascaded down 21.5 m at Hønefossen. Begna joins the Randselva river before discharges into Lake Tyrifjorden. The Begna is 213 kilometres (132 mi) long and has a high point of about 1,850 metres (6,070 ft). The Begna drains a watershed of 4,875 square kilometres (1,882 sq mi) and is the primary river in this watershed. 
The Association for Begna Watershed Control (Foreningen til Bægnavassdragets Regulering) is an association under the provisions of the Norwegian Watercourse Act. Its purpose is to protect members' common interests with regard to the use of water from the Begna basin used for power generation. The hydropower company operates 20 power plants on the Begna and Drammenselva below Tyrifjord. The association is responsible for maintenance and operation of dams, gates and stations along the Begna waterway. The plants are mainly located in Valdres.
- Rune Nedrud. "Begna". Store norske leksikon. Retrieved October 1, 2016.
- Erik Bjerck Hagen. "Mikkjel Fønhus". Store norske leksikon. Retrieved October 1, 2016.
- Geir Thorsnæs. "Hønefossen". Store norske leksikon. Retrieved October 1, 2016.
- Velkommen til Foreningen til Bægnavassdragets Regulering (Foreningen til Bægnavassdragets Regulering) Archived 2011-09-05 at the Wayback Machine
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