According to its statutes, the SMIDDEST has as its object “the coordination and implementation of any initiative, or joint action of its members, relating to the quality of the living environment, the environment, spatial planning, tourism, culture or economic development”, still linked to the Gironde Estuary.

Its missions cover several areas:

• The management of water and aquatic environments: it is the preservation of the environment with the SAGE and fight against the risk of flooding.
• Promotion and Development of the Estuary, to make the estuary a major sustainable tourism site on a national scale. The union carries out substantive actions (structuring and networking of actors, conducting studies, seeking funding, etc.), and promotional operations (design of an annual magazine, the Universe of the Estuary link, events , press reception, etc.).
• Guarding, management and reception of visitors to the Cordouan Lighthouse, the oldest lighthouse in France, listed as a Historic Monument since 1848 and the only lighthouse at sea in the world still inhabited.
• Finding and managing funding programs. The SMIDDEST thus managed and led two European LEADER programs (2001-2013) whose objective was to support the financing of local development projects in the fields of tourism, heritage, the environment and agriculture. The union has developed a new 2014-2020 strategy through which it tries to mobilize new funding for the coming period.