Gérardmer Lake, Glacial lake in Vosges, France

Gérardmer Lake sits in the Vosges mountains at an elevation of 660 meters (2,165 feet) and covers about 115 hectares (284 acres). At its deepest point it reaches about 38 meters (125 feet) and offers calm water surrounded by forested shores.

Gérardmer Lake is the largest natural lake in the Vosges, dammed by a hummocky terminal moraine that blocked the valley downstream after the Würm glaciation, roughly 80,000 to 10,000 BC. It is the third of the Valley of Lakes, after the cirque lake of Retournemer and Longemer in its glacier-carved basin. Written records call it the sea of Giralmer in 1593 and Grand Mer in the 17th century.

The lake's name comes from Saint Gérard, Bishop of Toul (935–994), and locals long called it simply "the sea". In high summer a lakeside festival features firework displays and wire sculptures decorated with flowers. A fireworks show is also held on the lake shore at 22:30 on Bastille Day.

A marked walking path circles the entire lake and offers various entry and rest points. Swimming zones are available during summer months, and many areas are easily accessible with parking and rest spots along the route.

Tens of tonnes of weapons and munitions were dumped in the lake's north-east sector. Between 1977 and 1994, divers from the Colmar demining centre carried out 12 clearance campaigns and removed 120 tonnes of munitions, roughly 100,000 pieces from the 1914-18 and 1939-45 wars. The lake was declared cleared to about 20 metres depth in 2014, yet the environmental group Robin des Bois estimates 70 tonnes remain.