Bay of Biscay

The Bay of Biscay, also called the Gulf of Biscay or the Gulf of Gascony, is a northeastern Atlantic gulf situated south of the Celtic Sea. It stretches along Spain’s northern coast from the French border to Cape Ortegal, and along France’s western coast from Point Penmarc’h down to the Spanish border. Its average depth is 1,744 meters (5,722 feet), with a maximum depth of 4,735 meters (15,535 feet).

In Spain, it is known as the Gulf of Biscay, while in France it is called the Gulf of Gascony. Historically, the Romans called it Sinus Cantabrorum, and the southern part is still locally referred to as the Cantabrian Sea. The English name comes from Biscay, a region on Spain’s northern coast that once represented the western Basque districts.

The continental shelf extends far into the bay in places, creating shallow waters that contribute to the rough conditions the area is famous for. Severe storms are common, especially in winter, and the bay experiences some of the Atlantic’s most violent weather, including abnormally high waves. Until recently, merchant ships frequently sank in these storms.

The International Hydrographic Organization defines the bay’s limits as a line from Cape Ortegal to Penmarch Point. The southernmost part is the Cantabrian Sea. Major rivers flowing into the bay include the Loire, Garonne, Dordogne, Adour, Nervión, and many others.

In late spring and early summer, a large fog triangle covers the southwestern half of the bay, reaching a few kilometers inland. As winter arrives, weather turns severe. Depressions often come from the west, moving toward the British Isles or the Ebro Valley, where they dry out and later reform as powerful thunderstorms over the Mediterranean. These depressions bring light but steady rain to the coasts, known locally by names like orballo or sirimiri. Rapid pressure drops can create powerful windstorms, such as Cyclone Klaus, that travel along the Gulf Stream at hurricane-like speeds. The Gulf Stream itself enters the bay along the continental shelf’s edge, keeping temperatures moderate year-round.

Major cities along the bay include Lorient, Vannes, Saint-Nazaire, Nantes, La Rochelle, Bordeaux, Bayonne, Biarritz, San Sebastián, Bilbao, Santander, Gijón, and Avilés.

Historically, the southern end is called the Cantabrian Sea in Spanish, from Estaca de Bares to the Adour River. The Romans named it Sinus Cantabrorum and Mare Gallaecum. On medieval maps, it sometimes appears as the Basque Sea. The bay has seen many naval battles: in 1592, the Spanish defeated an English fleet here; in June 1795, the British Channel Fleet and French Atlantic Fleet fought off southern Brittany; the USS Californian sank after hitting a mine in 1918; the SS Afrique was lost in a storm in 1920, killing 575; in 1943, HMS Glasgow and HMS Enterprise battled German destroyers; and from 1943 to the end of World War II, U-boat crews called the area the “Valley of Death” due to repeated RAF attacks. The U-667 struck a mine and sank in 1944 with all hands. In 1970, the Soviet submarine K-8 sank after a fire, killing 40 sailors and losing four nuclear torpedoes; no salvage was attempted due to the depth.

The Plaiaundi Ecological Park, a 24-hectare coastal wetland where the Bidasoa River meets the sea, hosts diverse flora and fauna, including migratory birds, reptiles, mammals, and insects. Car ferries from Gijón to Nantes or Saint-Nazaire, and from Portsmouth, Plymouth, and Poole to Bilbao and Santander, offer good opportunities to see cetaceans, and ORCA volunteers regularly monitor them.