In order to avoid siltation, floods, water overflow and / or drought, the SAH, (Hydraulic compagny) manages the water between the Loire, the Marais Breton and the Sea towards the Port of Collet.

51 municipalities are concerned with water management.

The importance is capital for the conservation of species and the preservation of the natural environment, the area being classified Natura 2000.

The roles of these winnowing are multiple: to take seawater at high tide to supply the salt marshes, to evacuate the rainwater at the end of winter to allow cleaning and cleaning of the marshes at low tide, to replenish the freshwater marshes in some places.