Sysenvatnet is a lake in the municipality of Eidfjord in Vestland county, Norway. The 10.24 km2 lake lies at the north end of the Sysendalen valley, about 8 km 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 Hydroelectric Power Station. The Sysen Dam can easily be seen from Norwegian National Road 7, which runs near the southern shore of the lake.