Sléttuhlíðarvatn is 0.76 km² in size and 14 m. The lake has char and good numbers of trout, usually rather small fish rather than good food fish. Sea-run char enter the lake to some extent, via a stream that flows out of the lake and merges with Hrolleifsdalsá, which is a good sea-run char river. The whole season is good fishing, but especially in May and June. It is best to fish on the east side of the lake, below the farms, where streams flow into the lake.