Batz-sur-Mer is a commune in the Loire-Atlantique department in western France. The commune is situated on a former island, which until arou…Batz-sur-Mer is a commune in the Loire-Atlantique department in western France. The commune is situated on a former island, which until around the 9th century was separate from the mainland at Guérande and the neighbouring island of Le Croisic. The territory of the commune is now part of the wild coast of the Guérande Peninsula with rocky cliffs, sandy beaches along the Atlantic Ocean and extensive salt marshes to the northeast and east.