Abstract-Water, fish and power. A century of management of the exchange between sea and lagoon in Camargue. The biogeophysica[ functioning of the Isle of Camargue is made of exchanges with the outside: water and sediments of the RhOne and the sea watershed have built i up the delta. The faunistical populatings which have made it famous (migrating fish and birds) are pledged by those exchanges. As soon as the middle of the XIXth century, the delta has been cut off from the river and the sea because of large development projects like dykes, sponsored by the State. Face to the resulting impoverishment of the environment, an artificial compensation of water exchanges has been created via some systems of water circulation to satisfy the needs of irrigation and drainage. This article aims to show that the famous 'natural environments" of the delta are nowadays regulated by all those development projects. The very particular functioning of that "anthropise" ecosystem, interact with the local social system and especially the fishermen. Standing away deliberately from a general dlscours on that question, a group of researchers gathering historians, hydrobJologists and sociologists has focused their demonstration on the relation between fish populatings of the Camargue, the history of the dyke to the sea and the management of a point of contact between the sea and the lagoon built up within the former.