Longerakvatnet or Longeraksvatnet is a lake in the municipality of Bygland in Agder county, Norway. It has a small dam on the southwest side to regulate the water level for hydro-electric power generation at a plant located down the hill. The lake discharges into the Longeraksåni river which flows into the Byglandsfjorden near the village of Longerak. The 3.4 km2 lake is located about 6 km southeast of the village of Lauvdal and about 10 km northeast of the village of Byglandsfjord.