 Located in the cwmwd of Malltraeth, Cors Malltraeth Marsh is situated on the western side of the Afon Cefni valley which crosses Anglesey parallel to the Menai Straits, approximately to the northwest.The habitat of Cors Ddyga on the eastern side of Afon Cefni has been reverted to wetlands and reeds.The wetland reserve is officially called RSPB Cors Ddyga.