Kleifarvatn is the largest lake on the Reykjanes peninsula in Iceland, situated in the southern part of the peninsula on the fissure zone of the Mid-Atlantic Ridge. The lake can be reached via a track, and there are two areas with high temperature that can be found not far from it: Seltún/Krýsuvík and another to the east. The lake´s greatest depth is 97 m. After the big earthquake in 2000, the lake began to diminish, and 20% of its surface has since disappeared.
The cracks that opened up in the earthquake have since then slowly filled again and by 2008 the lake had regained its previous surface level.