Hlíðarvatn is a generous and popular fishing lake. The peculiarity of the lake is that the water level changes a lot during the summer and therefore also the fishing spots in the lava between months. The lake is just over 4 km² in area and the maximum depth is about 20m. It is at about 75 m above sea level. There are both Arctic char and brown trout in the lake and it is common knowledge that there are at least two varieties of char in the lake. The fish can be big and brown trout have been caught in the water around and over 50 cm as well as large char, although most of the fish are around and over the pound. Fly fishing, worms, and spinners work well, but care should be taken not to get stuck in the lava bottom on the west side of the lake. Hlíðarvatn is best fished in the first half of the summer, but the fishing is good throughout the summer. Ice fishing is also practiced in the lake during the winter.