Celtic Sea

The Celtic Sea is an area of the Atlantic Ocean between the south coast of Ireland, the southwest coast of Wales, and the north coasts of Devon and Cornwall. It extends 645 km north-south (46.48° N to 52.28° N) and 560 km east-west (11.5° W to 4.192° W). The surface area is about 300,000 km².

The western boundary is considered to be the extreme west of Ireland. The approximate southern boundary is at the level of Brittany, following the continental shelf, also called the Celtic Shelf in the Celtic Sea area. On the coast of Brittany, the Celtic Sea meets the Bay of Biscay at the Pointe de Penmarch, which is also the southern limit of the Baie d'Audierne.

It is joined to the northeast by the Bristol Channel, to the east by the English Channel, and to the south and southeast by the Bay of Biscay. The Iroise in the southeast is part of the Celtic Sea.

The islands of the Celtic Sea include the Isles of Scilly and the Breton islands of Ouessant and Île de Sein. The island of Lundy lies on the border of the Bristol Channel.

Between the Celtic and Irish Seas runs the St George's Canal.