The White Sea magical lagoon between dunes and ocean

La Mer Blanche, a coastal lagoon sheltered from the Atlantic swell by a dune belt.

This unusual spot lies to the west of Mousterlin in the commune of Fouesnant. At low tide, birds scour the foreshore in search of molluscs, crustaceans and seaweed. Many species of fish also frequent this lagoon (sea bass, mullet and flatfish). This protected natural site is a treasure trove of biodiversity, popular with nature lovers and families looking for a peaceful stroll. Here, the calm of the water contrasts with the vigour of the nearby Atlantic.

The White Sea A rare and changing landscape

Located to the west of the Pointe de Mousterlin in Fouesnant-les Glénan, the Mer Blanche is a coastal lagoon: an area of salt or brackish water separated from the sea by a dune belt. This coastal lagoon is sheltered from the Atlantic swell by a dune belt where the water ebbs and flows with the tides, making the site lively and changing, home to a wide variety of animal and plant species. At low tide, birds roam the foreshore in search of molluscs, crustaceans and seaweed. Many species of fish also frequent this lagoon (sea bass, mullet and flatfish).

Booklet for the respectful visitor - Mousterlin

A photogenic setting all year round

The White Sea reveals a different face depending on the time of day, the season and the tide. It’s an extraordinary natural photography spot, bathed in soft light and open to vast horizons. This astonishing site, peaceful and ever-changing, creates a unique bond between man and nature. With each visit, the Mer Blanche reveals a little more of itself, but it also demands our kindness and respect.

A little history the origins

Between the Pointe de Mousterlin and the Pointe de Beg Meil, this dune system, also known as Le Letty, forms a natural boundary between the Mousterlin marsh and the sea. The natural channels that once divided the dunes, bringing salt water to the marsh, have disappeared over time as the sand has shifted. The dunes now form a continuous line of sand.

Connected directly to the ocean by a gully, the Mer Blanche’s water is completely salty. The coastal lagoons play an essential role for many species of fish and contribute to the quality of the water.

Flora adapted to sand and water
Coastal flora is adapted to sand and salt water. On the dunes, oyats, dune spurge and sea bindweed fix the sand. At the edge of the lagoon, saltwort and sea plantain resist the salinity.

A discreet but very present fauna
At low tide, birds use the lagoon as a feeding ground throughout the year. Many species, such as the long-necked grebe, frequent the Mer Blanche. Small aquatic fauna also inhabit the shallow waters.

The entire coastline stretching from the Mer Blanche to Beg Meil, including the Mousterlin marsh, is classified as a protected area.
of Mousterlin, is classified Natura 2000.

Our ideas for walks At the White Sea

Mousterlin et la Mer Blanche

De la Mer Blanche au marais de Mousterlin

Autour du Marais de Mousterlin

All the walks

The White Sea Locate

Responsible visit Our advice

La Mer Blanche is the perfect place for a peaceful stroll, with the family or on your own. The site offers an accessible, well-marked walking loop of around 5 km. Try to get there at high tide or low tide to watch the movement of the water and the activity of the birds. Recommended departure point: Kerler beach car park (Mousterlin).

Times: Free access all year round, except during high tides or conservation work.
Cycle access: Accessible by bike, but prefer to walk the path.
Accessibility: Limited access for people with reduced mobility (sandy ground).
Guided tours: Organised from time to time with nature guides or local associations.
Good to know: Interpretation panels line the trail to help you discover the fauna, flora and history of the area.

Stay on the paths: trampling on the dunes and wetlands damages them.
Avoid the nesting areas indicated in spring.
Be quiet and patient: nature is best observed in peace and quiet.
Keep dogs on a lead, especially during the breeding season.
Don’t swim in the lagoon (stagnant water, silt).
Don’t pick up anything: even a flower or a shell contributes to the ecosystem.

Other sites To explore

The Mousterlin Marsh

The cove and woods of Penfoulic

Natural areas