Þórisvatn, the second largest lake in Iceland, 70 km2, 109 m deep. This lake is regulated and may rise by as much as 5 meters, reaching 80 km2. Its upper end is cut in two by the mountain Útigönguhöfði, forming two bays. The shores are mostly steep and desolate. Formerly the outlet was Þórisós, but there is now a regulated outlet down to the power station of Sigalda.