Lake Skjalftavatn has an area of about 9 kmē. It is rather shallow and 15 m above sea level. Prior to the creation of the lake in 1974 the area was a sand and gravel desert, which had been reclaimed and turned into fields and meadows.

During the years 1975-1984 vast areas were changed by the plate tectonics. Nine eruptions took place farther south and the lake's surroundings changed considerably. Its discharge are rivers Stora and Litla. The former spills into the lagoon Arneslon and then to the sea. Road no. 85 passes the lake to the south. The catch of the lake and its discharges consists mainly of sea trout, sea char and occasional salmon.

The distance from the capital is 533 km by the Whale Bay tunnel and 53 km from Husavik.