Lake Kleifarvatn is in a depression between two ridges and the barren, volcanic surroundings are uniquely beautiful. It is a lake with no visible drainage and fluctuating water level due to rise and fall of ground water level. Kleifarvatn is the largest lake of the Reykjanes peninsula, about 9 kmē, and 97 meters deep. There is good Char fishing in the lake.
The lake is supposed to be the home of a large USO (unidentified swimming object), claimed to be occasionally seen.