Oberaarsee is a hydroelectric reservoir in the Grimsel area, part of the municipality of Guttannen, Switzerland.

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.

This article related to a lake in the canton of Bern is a stub.