Lac de Grand-Lieu

Lac de Grand-Lieu is a lake located to the southwest of Nantes, in the Loire-Atlantique, France, and almost entirely in Saint-Philbert-de-Grand-Lieu. At an elevation of 5 m, its surface area is 62.92 km2, making it the largest lake in France in winter, but second after Lac du Bourget in summer.

The lake is classified as a Local Nature Reserve, and use of boats on the lake are prohibited for all but a small number of licensed professional fishermen.

Source: Wikipedia