The Menai Strait fish weirs are historically important fishing traps used in the fast-flowing tidal waters of the Menai Strait, which separates Anglesey from the rest of North Wales. The strait was particularly well suited to utilising fish weirs. The tidal waters pull huge volumes of water past the coastline with every tide, and the weirs and traps enabled fish to be concentrated into small holding areas from which they can be readily caught. Such methods are thought to have been used from earliest times, but the submerged and standing remains along both the Anglesey and Gwynedd coasts are from medieval and post-medieval periods, and in some cases were still in use into the 20th century.