What is "maridalsvannet"

Maridalsvannet is a lake in Maridalen, Oslo, Norway. It is the largest lake in the municipitality of Oslo, and serves as the main drinking water supply for the city. The lake drains via the river Akerselva to the Oslofjord. The primary inflows are Skjærsjøelva and Dausjøelva. The Hammeren Hydroelectric Power Station exploits the fall from Skjærsjøen to Maridalsvannet.