Cemlyn Bay is a beach approximately 700 yards wide, situated on Anglesey's north-western coast between the headlands of Cerig Brith and Cemlyn Head. It is owned by the National Trust and is mostly a shingle ridge which blocks off a lagoon of brackish water. Some sand is revealed at low tide. Car parking is free and car parks are situated at both ends of the beach. The western end has a small slipway.
The lagoon is an important breeding area for sea-birds including the common, Arctic, roseate and sandwich terns, plovers and sandpipers.