The Site is a large estuarine complex of alluvial marshes, mudflats, estuarine waters, rivers, peatlands, and a network of ditches and open water bodies which converge into the Grand’Mare natural pond. Marais Vernier, a former meander of the Seine River, holds the largest peat deposit in France. The Risle coastal river is a transition zone between saline and fresh water, which supports intertidal habitats of great importance for fish. The Site as a whole regroups 43 species of fish, of which 32 are indigenous, and provides important migratory paths or reproductive grounds for a number of species including the globally endangered European eel (Anguilla anguilla), the northern pike (Esox lucius) and the lamprey (Lampetra fluviatilis). The wetland provides wintering grounds for several species of waterbirds including large numbers of European golden plover (Pluvialis apricaria) and northern lapwing (Vanellus vanellus). Human activities are focused on agriculture, hunting and fishing. The Site holds important social and cultural values associated with a history of wetland-related traditional practices which maintain this mosaic of habitats and the associated biodiversity. Cottages on the Site showcase the traditional use of reeds for thatching. The main threats to the Site relate to drainage in Marais Vernier, and the poplar tree plantations, roads, and utility and service lines crossing the Site. A management plan is in place for the Natura 2000 Site, which covers the whole Ramsar Site area.