The biggest water reservoir in the area - the Primstalsperre in Nonnweiler - was completed in 1982. With a water surface of 96. 4 hectares, this lake is a lot smaller than the Bostalsee lake, but with a depth of 45 meters it has a capacity of approximately 20 million square meters. The lake is fed by the Prims and the Altbach which unite in the reservoir. The two Hunsrück streams have an excellent water quality, which was required for the initial planning of a water reservoir for the northern Saarland and Hermeskeil on the Rhineland-Palatinate side. Today, the water is, among other things, used for the low water improvement of the Prims. Via a pipeline water is fed into the Blies as well. The dam has a length of 306 meters and a height of 62 meters. At the foot, the dam  has a width of 290 meters, on the crown one of 10 meters. The water intake tower, the funnel-shaped channel spillway and the two plunge pools at the outlet are part of the structurally engineered systems to be seen at the Primstalsperre.

The Primstal reservoir is idyllically situated in the Hochwald landscape and is a place of peace. It is surrounded by a twelve-mile circular path - a meeting place for hikers and bikers! Worth-seeing is the reconstructed “Züscher Hammer” which once was the largest iron mill in the Hunsrück.

A section of the circular route is the 5.9 km-long planet trail. On a scale of 1:1 billion, the planets of our solar system are shown as models. Information panels along the models explain the visitors the dimensions and the interplay of sun, moon and earth. A true experience for the whole family!

The artwork at the dam was created by the Saarland artist Paul Schneider. The sculpture represents a reference to the Celts, who worshipped the elements of water, air, fire and earth. The artwork is focused on the movement of the sun. Its red color is reminiscent of the fire.