The lake of Longemer is surrounded by mountains and forests. Its waters are supplied by the Vologne, a river whose source originates not far from there, at the foot of the Hohneck. Oblong in shape, it is aptly named Long Sea. It is also called the mirror with a thousand reflections because of its ever-changing morning brightness. The Lac de Longemer is one of the largest in the Vosges mountains and is classified as a protected natural site.