Lac de Grand-Lieu (French: [lak də gʁɑ̃.ljø]) 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 (16 ft), its surface area is 62.92 km2 (24.29 sq mi), making it the largest lake in France in winter, but second after Lac du Bourget in summer.

[2] Except during the winter floods, it is only accessible from a few locations, such as at Bouaye in the north, at Pierre Aigüe in Saint-Aignan-Grandlieu and la Chevrolière in the east.

The zone where the junction with The Tenu occur was made close to the island Marguerite (area which was originally called the three channels)[6] During the system of feudalism, the lake was owned by the lordship of Grand-Lieu.

From 1387 the rent has stopped[7] The Machecoul-Gastineau then take possession of the rights which they do not have and expropriate the property title[8] The control of this domain, with the absence of firm land, is not without consequences: the population around the city of Nantes receive fresh water fish from the lake.

[11] In 1809, the Comte August de Juigne, who is the holder of the rights on the lake, project to drain and dry it in order to use it to grow crops.

At that time is type of initiative was common, relying on the economic argument but also on the problem related to health that wetlands can bring to the close population.