Sysenvatnet (English: Lake Sysen) is a lake in Eidfjord Municipality in Vestland 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 Vøringsfossen waterfall. The lake is dammed on the south end by a large stone embankment, which is used as the main reservoir for the Sima Hydroelectric Power Station. The Sysen Dam can be seen from Norwegian National Road 7, which runs near the lake's southern shore.