Sysenvatnet is a lake in the municipality of Eidfjord in Hordaland county, Norway. The 10.24-square-kilometre (3.95 sq mi) lake lies at the north end of the Sysendalen valley, about 8 kilometres (5.0 mi) east of the famous Vøringfossen waterfall. The lake is dammed on the south end by a large stone embankment, and the lake is used as the main reservoir for the Sima power station.