Rivers Thjorsa and Tungnaa were dammed just east of Mt Sandafell, about one kilometre to the north of their confluence during the years 1982-84, and the man made lake was created.  Its surface lies 297 metres above sea level.  The construction work of the hydroelectric power plant did not start until in the spring of 1997.  The first generator was engaged in 1999 and a year later the power plant was delivering full capacity.