[2] The bay of Bourgneuf is a vast maritime arc on the French Atlantic coast running from the Pointe Saint-Gildas (south of the Loire estuary) to Beauvoir-sur-Mer and is enclosed by the island of Noirmoutier up to the île du Pilier.

It thus includes the south coast of the Pays de Retz, the shore of the Marais breton ('Breton Marshes') and the east coast of Noirmoutier, the latter being connected to the mainland by the notable Passage du Gois and, to the south, the bay connects to the north of the Bay of Biscay by the Strait of Fromentine, crossed by the Noirmoutier Bridge since 1971.

[5] The prosperity of the towns of the bay declined in the 18th century with the reduction of trade due to the silting that hampered production and the navigation of large vessels.

Under the Ancien Régime, this region was the centre of a significant smuggling operation operated by the coureurs de lune (moon runners) who trafficked illegal tobacco, salt, wines, liquour, and Indiennes, on foot, horseback or aboard three-masted lighters known as "chattes", constantly trying to evade capture by customs officers.

Smuggling was principally operated from the isles of Bouin, Noirmoutier and île d'Yeu, exacerbated by the islands' tax-exempt status at the time.

[10] According to Natura 2000, the Marais Breton forms part of a larger geographic zone which also includes the Pays-de-Monts National Forest and the island of Noirmoutier.