[3] The 18th-century maps identify "Passage de l'Iroise" as the channel leading north-west from Pointe Saint-Mathieu and keeping south of Ushant (Ouessant) and the Ponant Islands.
[3] From the 19th century, the term Iroise encompassed all the sea along the west coast of Brittany between Ouessant and Sein.
[3] While this remains the limit used by mariners,[4] some twentieth-century sources have used mer d'Iroise to denote the entire Celtic Sea as far as Ireland and Great Britain.
[4][8] The Pont de l'Iroise bridge was opened in 1994. in maritime weather forecasts by Météo-France and Spain's AEMET, "Iroise" denotes the sea area east of a line from 48°27′N 6°0′W / 48.450°N 6.000°W / 48.450; -6.000 to 47°30′N 6°0′W / 47.500°N 6.000°W / 47.500; -6.000; this corresponds to the northern part of the UK shipping forecast sea area of Biscay.
Owing to the hazardous conditions at sea, the high density of shipping and a number of shipwrecks in recent years, the French authorities have introduced special search and rescue operations.
These rely on vessels such as the Abeille Bourbon, as well as a number of large lifeboats based in the ports of Douarnenez, Camaret, Le Conquet, Molène and Ushant.
The Iroise Marine Park covers an area of 3,550 km2 (1,370 sq mi)[10] from latitude 48°31′N (the north coast of Ushant) and latitude 47°59′N (south coast of the Île de Sein), the mainland coastline to the east except for the Rade de Brest, and the 12-nautical-mile (22 km) limit on French territorial waters to the west.