The marshes of Guérande and Marennes-Oléron on the French Atlantic coast are some of the most complex landscapes built by human in ancient times. Once created, these wetlands have been used for sea salt production. A complex labyrinth of man-made waterways, dams and pools is feed by the tides of the sea. In spring, the farming cycles begins by flooding the pools. A slight, constant change in level allows the water to flow into the evaporation ponds, which act as a reserve. Once the water evaporates by sun and wind, the seawater reaches a concentration level at which the salt crystallizes and becomes harvestable.

Until the 19th century, the production of salt gradually declined. In response, the inhabitants turned to oyster farming and slowly transformed the salt gardens into oyster farms. The oysters are bred in beds 5 km out at sea, then matured in the shallow ponds. This landscape is a prime sample of how human have adapted to a changing economy market by using natural circumstances.