Lake Reyðarvatn is in Borgarfjarðarsýsla, from the bottom of Lundarreykjadalur. It is 8.3km² in area and lies at an altitude of 325m. It is best to get to the lake from the road Uxahryggjarvegur. Into the east part of the lake runs Reyðarlækur from Lake Stórra-Brunnvatni. From the northeast two rivers run into it, Leirá and Fossá. The well-known salmon river, Grímsá, flows out from the lake to the northwest. Reyðarvatn has good numbers of Arctic char and some are small (dwarf) char. Fish of more than 12 pounds have been caught, but the most common size is 1-2 pounds, excluding the very small (dwarf) char. There are many good fishing spots all around the lake. One of the best fishing spots is where Grímsá runs from the lake and another where Fossá runs into the lake.