The granite ridge of the Reisberg separates the lac Blanc (White lake) from the lac Noir (Black lake). Both communicate by a pumped storage system that regulates their level. Lac Noir is nestled at the bottom of a glacial cirque of high granite cliffs. Its ground is covered with black peat bogs, which gives it its deep color. Surrounded by large fir trees, the lake's dark decor attracted film directors Jean-Pierre Mocky and Régis Wargnier for the filming of two movies.