Lake Þiðriksvallavatn is in Hólmavíkurhreppur in Strandasýsla. It is 1.45 km² in area, deepest 47 m and at 73 m above sea level. To the west of it is Þiðriksvalladalur, well-vegetated and fertile. At the end of the lake in the valley are the deserted farms Þiðriksvellir and Vatnshorn. River Þverá flows from the lake to Steingrímsfjörður and is powerful. A track to the lake goes from highway 61 a few kilometers south of Hólmavík. The environment is very green and is considered beautiful. The lake has decent Arctic char and plenty of good brown trout, lots of fish. It is owned by Hólmavíkurhreppur.