the beddmanarch–cymyran site comprises the area of coastal salt-marshes, mud-flats and shallow coastal water lying between holy island and the mainland of anglesey. this includes the cymyran strait (sometimes called the holy island strait), the tidal reaches of the afon alaw to the east and extends northwards to porth penrhyn-mawr. there are two crossings over the water that makes up the site, four mile bridge (road and pedestrian) and the stanley embankment (road, rail and pedestrian). the area between the two bridges in known as the "inland sea".