Lagoons are saline or brackish water bodies partially separated from the adjacent sea. Coastal lagoons are a rare habitat in Wales with the largest, and best known, found at Cemlyn Bay on Anglesey (see image). The coastal lagoon at Cemlyn Bay was originally a percolation lagoon that has also been sluiced. It is separated from the sea by a shingle bank with water exchange occurring mainly through the sluice and by percolating through the shingle. The lagoon is best known for supporting a large breeding colony of sandwich (Thalasseus sandvicensis), arctic (Sterna paradisaea) and common terns (Sterna hirundo), with roseate terns (Sterna dougallii) also breeding on occasions. The flora of the shingle bank is also notable in a Welsh context, supporting good populations of sea kale (Crambe maritima) and yellow-horned poppy (Glaucium flavum).