The Thau Pond is the largest lagoon in the regional territory and is classified as an area susceptible to eutrophication. Its shellfish farming vocation is important with 10 % of the national oyster production and 2000 related jobs. Fishing is as well represented as well as water sports and boating. In addition, the site is known for its aquatic fauna and flora. Microbiological pollution can disrupt the biological balance of the lagoon and call into question the economic activities of the territory that are strongly related to the quality of the water in the environment. The watershed’s polluting inputs accumulate in sediments and are regularly suspended. This project will respect the eligible microbiological flows in rainy weather for the Marseillan sector, i.e. compliance with a maximum level of microbiological input to the lagoon to enable the maintenance of activities (conchyliculture, fishing and bathing).