Cemlyn Bay

Cemlyn Bay is a bay on the northwest coast of Anglesey, North Wales, approximately 2.5 km west of Wylfa nuclear power station, within the community of Cylch-y-Garn.

Separated from the bay by a shingle beach is a brackish lagoon, which is fed by a number of small streams. A weir at the western (Bryn Aber) end of the beach regulates the lagoon's water level.

The site was designated a Site of Special Scientific Interest in 1958, and is currently part of the Anglesey Heritage Coast and the Isle of Anglesey Area of Outstanding Natural Beauty. The Cemlyn estate is owned by the National Trust; the lagoon and its immediate surrounds comprise Cemlyn Nature Reserve (25.2 ha in extent, set up in 1971 and leased by the North Wales Wildlife Trust). The Anglesey Coastal Path passes through it.

On islands at the western end of the lagoon, there is an important tern colony, with the only breeding Sandwich terns in Wales. The numbers of breeding Sandwich terns have increased to around 1,500 pairs in recent years, making Cemlyn the third-largest colony in the United Kingdom. Arctic and common terns breed here regularly in smaller numbers but roseate tern now only occasionally. For this reason Cemlyn has been designated as part of the Ynys Feurig, Cemlyn Bay and The Skerries Special Protection Area along with two other nearby sites, Ynys Feurig and The Skerries, and all three are also classed by BirdLife International as an Important Bird Area. Birds interchange regularly between all three sites, and form part of a larger Irish Sea tern population together with birds at sites in Ireland such as Rockabill Island. The tern colony is wardened from May to August.

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