Oberaarsee is a hydroelectric reservoir in the Grimsel area, part of the municipality of Guttannen , Switzerland . Its surface area is 1.47 km2 (0.57 sq mi). The Oberaar dam was completed in 1953, and is operated by Kraftwerke Oberhasli . It is drained by the Oberaarbach, which flows into the Grimselsee .

The Oberaar glacier is located west of the lake.