Lake Longemer is a lake in Vosges, France. It sits in a basin which was made by a glacier. Surface area is 76 ha and it is 1950m long, 550m wide and 34m deep; Altitude is 736m. A small chapel dedicated to Saint Florent is located on the western shore of the lake. It already existed in the middle of the 15th century, and was rebuilt in 1449. The chapel fell into ruins and was rebuilt under the name of Saint-Laurent des Graviers in 1727. It occupies the place of an Oratory dedicated to Saint Bartholomew which, according to a legend, was the hermitage erected in 1056 by the pious hermit Bilon, a former officer of Duke Gerard I of Lorraine.