Ay, Coastal river in Manche, France

The Ay is a coastal river in Normandy that winds through the Manche landscape and flows toward the English Channel. It creates a transition zone where freshwater streams meet tidal influences from the sea.

The only recorded river works are tide gates (portes à flots) installed between 1830 and 1835, which regulated the lower course near the sea. The river rises at 122 m on the boundary of Gratot and La Vendelée under the name Champeaux, and reaches the Channel through the havre de Saint-Germain-sur-Ay after passing Lessay.

The river's name is written Ay but pronounced "é". Its lower course ends in the havre de Saint-Germain-sur-Ay, a tidal inlet of dunes, salt marsh and mudflats that forms part of the 4,140-hectare Natura 2000 site "havre de Saint-Germain-sur-Ay - landes de Lessay", which also covers heathland and bogs upstream.

Multiple access points along the river allow visitors to fish, walk trails, or observe wildlife year-round. Conditions for these activities vary with water levels and tidal cycles.

The Ay's small basin, only 154 km², gives it a low flow of about 1.5 m³/s at its outlet, yet it feeds the 4,140-hectare Natura 2000 site "havre de Saint-Germain-sur-Ay - landes de Lessay". That site holds 24 habitats of European interest, including wet heaths with cross-leaved heath and ciliated fringed heath, plus 30 protected plants such as the dune helleborine.