Lysakerelven (also known as Lysakerelva, in either case meaning "the Lysaker River") is a river in Norway that forms the boundary between the municipalities of the capital city of Oslo and Bærum.The river by this name has its source in Bogstadvannet, though the source is further up, at Langlivann, and Søndre and Nordre Heggelivann in Oslomarka, the forests surrounding Oslo.