Lake Thorisvatn has an area of 0,48 kmē. Its greatest depth is 3-4 m and it is situated at 59 m above sea level. The main road passes its southern end.

Lake char fries were released into it in 1967 and they have thrived quite well. According the legend the lake was fishless up to that year because a ogress, whose husband drowned in the lake, cast a spell on it, saying it would remain fishless from then on. The distance from the capital is about 737 km.