Dexter Marsh is a 1,350-acre (5.5 km2) marsh located at the eastern end of Lake Ontario in Dexter, New York. It was declared a National Natural Landmark in May 1973. The marsh is managed by the New York State Department of Environmental Conservation as the Dexter Marsh Wildlife Management Area. The marsh is a popular fishing and trapping area as well as a migratory bird layover. Lacking barrier beaches, it is directly exposed to Lake Ontario's winds and waves. It is a relatively undeveloped bay-head area on the Great Lakes.