Gravatnet is a lake in the municipality of Sirdal in Agder county, Norway. The 5.33 km2 lake is located about 9 km north of the small village of Lunde. The lake lies immediately south of the lake Valevatn, which flows out into Gravatnet. The water in Gravatnet is stopped by a dam on the south side. The water is regulated at an elevation of 660 m and it flows out through the small river Gravassåni which is a tributary of the big river Sira.