The Förrevass dam is a concrete pond with a flood, and is one of fourteen dams that contain the artificial lake Blåsjø. It extends over the Förrejuvet, and regulates the Forreåna river. With a volume of about 255,000 m³, it is the largest concrete dam in Norway. It is about 1300 m long. In 1989, the dam received the honorary prize Concrete Board. No reinforcing steel was used in the construction, and since there was no sand available nearby, stone was crushed for use in the concrete. The boundary between the municipalities of Suldal and Hjelmeland goes in Førrejuvet and the dam is thus located in both municipalities.