Summer is settling in, the days are getting longer, and a familiar breeze is blowing across Southern Brittany. For all boating enthusiasts and lovers of the sea, the signal has been given: it’s time to launch the boats! The Gulf of Morbihan (literally "Little Sea" in Breton) is emerging from its winter slumber. Sails are unfurling, engines are purring softly, and hulls are once again cutting through water of surprising clarity. Here, boating is an art that consists of hopping from one island to another—from Arz to the Île aux Moines, via the countless secret islets that dot this 115 km² maritime labyrinth.
But the brilliance of this enclosed little sea hides a fascinating oceanographic secret: its waters are completely renewed approximately every 10 days. Dive into the heart of a unique ecosystem where the moon, the currents, and the oysters set the pace.
The great vortex: a sea that breathes to the rhythm of the tides
Seen from above, the Gulf of Morbihan looks like a large lake connected to the Atlantic Ocean by a single, narrow strait barely 900 meters wide, located between Port-Navalo and Locmariaquer. It is through this narrow gateway that everything happens.
Twice a day, the Gulf "breathes" to the rhythm of the tides
- The flood (the incoming tide): The ocean rushes forcefully into the Gulf to fill this immense basin.
- The ebb (the outgoing tide): The Gulf empties out to sea again.
Because the volume of water to be moved is colossal and the passage extremely narrow, this creates formidable currents. The boats that rush through it must be careful: as soon as they enter the Port-Navalo strait, the speed of the water can exceed 4 meters per second.
Zoom in on the Jument current:
If you pass this first obstacle and head east towards the Île aux Moines, you will face the true master of the area. It is precisely between the island of Berder and the island of la Jument that the legendary Jument current unleashes itself.
Considered the second most powerful tidal current in Europe, it is impressive in its technicality. During high tidal coefficients, its peak speed reaches 9.1 knots (or nearly 17 km/h or 4.68 m/s)! While this current is feared by novice pleasure boaters, it is a delight for thrill-seekers: sea kayakers love it and use it like a real treadmill or a natural surf spot to glide across the water at full speed.
Did you know? The association of the horse with marine power dates back to antiquity with the god Poseidon and his sea steeds. In Brittany, this symbolism has remained very strong to depict the indomitable power of the ocean (as with the Jument lighthouse at Ouessant or the Penmarc'h headland, which means "horse's head"). In the Gulf, la Jument lives up to its name: a wild and galloping force!
The 10-day miracle
Thanks to the violence and regularity of these tidal flows, an exceptional phenomenon occurs: the water of the Gulf of Morbihan is completely renewed approximately every 10 days. This constant mixing and natural cleaning prevent the waters from becoming stagnant, ensuring perfect oxygenation and remarkable purity. It is this perpetual current that makes the Gulf an environment of incomparable ecological richness, where nutrients from the open sea are constantly reinjected inland.
The queens of the Gulf: an oasis for oysters
This prodigious mixing makes the life of an emblematic inhabitant of the area a delight: the oyster. Rocked by the ebb and flow of the tides, nourished by phytoplankton rigorously renewed by the currents, the oyster beds of Morbihan thrive in ideal conditions. The Gulf is, moreover, historically the cradle of flat oyster farming in France.
Today, Morbihan (combining the Gulf and adjacent bays such as Quiberon) is one of the major pillars of French seafood cuisine. The Southern Brittany basin alone represents approximately 10 to 12% of the total production of cupped oysters consumed in France, and climbs up to nearly 50% for the prestigious and rarer flat oyster.
Every year, approximately 10,000 tons of shellfish are pampered by local oyster farmers before ending up on the tables of the French, from the small bistro in Vannes to the great restaurants of Paris.
At your helm!
The renewal of the water purifies the landscape with every tide, offering shades of blue and green that change every hour. So, whether you prefer paddleboarding, sea kayaking, classic sailing, or modern sailboats, take advantage of the beautiful weather to launch.
Sail to the rhythm of the currents, play with la Jument, dock at an island beach, and end your day as a skipper in an oyster farm, with a dozen ultra-fresh oysters on your plate.
That is the magic of the Gulf of Morbihan.
Check out the Vannes Tourisme website for more info: https://www.golfedumorbihan.bzh/mer/le-courant-de-la-jument/