Réserve naturelle nationale du marais d'Yves, National nature reserve in Yves, France.

The Réserve naturelle nationale du marais d'Yves is a 192-hectare national nature reserve at the bottom of the Baie d'Yves, a diamond-shaped area about 3 km long and 0.8 km wide. It combines mudflats, dry dunes and dune slacks, marshes and reedbeds, wet grasslands, tamarisk hedges and thickets. A concrete water-control structure with rusted threaded rods stands at the edge of the waterway.

The reserve was established in 1981 after local efforts prevented real estate development in the 1970s. Its protected status has preserved this coastal area from commercial expansion ever since.

The Maison de la réserve, opened in 1987, runs guided visits into the reserve, whose access is regulated. The bay is one of France's main sanctuaries for migratory birds: in winter it holds about 20,000 waders, 1,500 ducks and several hundred greylag geese, and 250 bird species frequent it. Highland cattle and horses graze the wet grasslands where white storks nest.

The best time to visit is during the bird migration seasons when the reserve hosts the most species. The site is accessible on foot or by bicycle, with several entry points available for exploration.

The land was underwater during Roman times, which shaped the geological features visible today. This ancient submerged past explains the varied habitats that make the reserve so attractive to wildlife.