Le Rostu in the heart of the Mès salt marshes

This hike is located in Mesquer, in the hamlet of Rostu.
The Bassin du Mès is an area where salt marshes have been created for centuries and were once highly developed. They are fed with seawater by channels leading from the "Merquel - Rostu - Pen-Bé" traicts, which are an enclave of the sea between the Pointe de Pen-Bé and the Pointe de Merquel. Oyster and mussel farming have also developed in this area. There are some beautiful views to be discovered.

Details

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  • Walking
    Activity: Walking
  • ↔
    Distance: 7.13 km
  • ◔
    Average duration: 2h 05 
  • ▲
    Difficulty: Easy

  • ⚐
    Back to start: Yes
  • ↗
    Ascent: + 10 m
  • ↘
    Descent: - 10 m

  • ▲
    Highest point: 14 m
  • ▼
    Lowest point: 2 m

Photos

Description of the walk

Go down to the car park near La Salorge on Rue de Rostu.

(S/E) Head towards Île de Rostu for 200 metres until you reach a crossroads.

(1) Take the path on the right that leads to the fisheries. This was once a strategic location, as there is a loading dock on the Pont d'Arm estuary (see photos and comments). Then retrace your steps for a few dozen metres.

(2) Take the path on the right where there is a clearly visible sluice gate and continue along the embankment, going around an active salt marsh until you reach a gravel pit.

(3) Cross this gravel pit, which leads to a remarkable spot called "La Fouillarde": a very pretty view of the entire stretch, with Pointe de Merquel and Pointe de Pen-Bé on the left. Walk along the beach and continue on the path that leads to it until you reach the first junction of the circular route.

(1) Turn right onto a wooded path (barrier at the entrance) that leads to Île de Rostu: beautiful view, with benches for resting.

(4) Return to the junction.

(1) Turn right and return to the start of the walk.

(S/E) Turn right onto a path that runs alongside several salt marshes and mudflats to Kervarin.

(5) Continue straight ahead to visit this old hamlet where salt workers and fishmongers once lived.

(6) Turn back.

(5) Bird observatory, beautiful view of the hamlet of Kervarin and the Mes basin. Turn right onto the small path that runs alongside a stream, cross two footbridges and continue until you reach Rue du Moello.

(7) Turn left into the private housing estate of Rostu, then follow the road on the right (Allée du Bois des Chênes) which leads to Rue de Rostu. Follow it to the left and take thefirst street on the right, Chemin de la Chouette.

(8) At the end of the path, turn left onto a trail that runs alongside mudflats and ends at Rue de Rostu. Follow it to the right to return to the Salorge car park (S/E).

Waypoints

  1. S/E : km 0 - alt. 4 m - Salorge car park
  2. 1 : km 0.21 - alt. 4 m - Crossroads of the circular loop
  3. 2 : km 0.89 - alt. 3 m - Saltwater sluice gate - Mès (fleuve)
  4. 3 : km 1.33 - alt. 3 m - Gravel pit for plovers
  5. 4 : km 2.22 - alt. 3 m - Rostu Island
  6. 5 : km 4.03 - alt. 3 m - Bird observatory
  7. 6 : km 4.28 - alt. 4 m - Hamlet of Kervarin
  8. 7 : km 5.32 - alt. 14 m - Ruse du Moello
  9. 8 : km 6.08 - alt. 4 m - Vasière de la Chouette
  10. S/E : km 7.13 - alt. 4 m - Salorge car park

Notes

TheGR®34, which starts at Mont Saint-Michel and runs along the Brittany coast to Saint-Nazaire, passes through this area.

NB: please respect this fragile environment and the work of the salt workers. Stay on the path and never go down into the salt marshes.

Worth a visit

The fisheries on the Boulay tidal flat are private and are used for fishing with square nets at high tide.
On the left is a loading quay. This quay, accessible to boats at high tide, was used to transfer goods. Initially, it was used to export salt to ports (Saint-Nazaire), but also to import stones for construction at that time.

The tidal flats and mudflats are also places where migratory birds like to stop at certain times in autumn and early spring. You can see: common shelducks, brent geese, oystercatchers, godwits, egrets, curlews, avocets, stilts, plovers, turnstones, common terns, herons, cormorants and several species of gulls.

Always be cautious and plan ahead when you're outdoors. Visorando and the author of this route cannot be held responsible for any accidents occurring on this route.

The GR® and PR® markings are the intellectual property of the Fédération Française de Randonnée Pédestre.

Reviews and comments

4.3 / 5
Based on 10 reviews

Reliability of the description
4.3 / 5
Ease of following the route
4.2 / 5
Route interest
4.4 / 5
Michnou
Michnou

Overall rating : 4.3 / 5

Date of your route : Jan 11, 2026
Reliability of the description : ★★★★☆ Good
Ease of following the route : ★★★★☆ Good
Route interest : ★★★★★ Very good
Very busy route : No

A very nice route, but it's a shame we did it in the rain and on very muddy and slippery paths.
We'll have to do it again in sunny weather and on dry paths to fully appreciate it.

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User 27617799

Overall rating : 3.7 / 5

Date of your route : Sep 22, 2025
Reliability of the description : ★★★★☆ Good
Ease of following the route : ★★★★☆ Good
Route interest : ★★★☆☆ Average
Very busy route : No

It took me this second hike to understand the subtleties of the map

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BrandO33
BrandO33

Overall rating : 3.7 / 5

Date of your route : Aug 12, 2025
Reliability of the description : ★★★★★ Very good
Ease of following the route : ★★★★☆ Good
Route interest : ★★☆☆☆ Disappointing
Very busy route : No

Not bad, well-designed and well-documented route.
But for me, there was too much tarmac, especially in the second part of the route (points 5 to 8)
The main interest of the hike lies in the first loop, which is also the shortest (points 1 to 4)

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ager44
ager44

Overall rating : 5 / 5

Date of your route : Jul 18, 2025
Reliability of the description : ★★★★★ Very good
Ease of following the route : ★★★★★ Very good
Route interest : ★★★★★ Very good
Very busy route : Yes

Superb hike in the sunshine. The sun was shining during the first part, but the wind made it pleasant. Don't forget to bring trousers, as the trail is overgrown with grass and thorns at this time of year. Easy walk, starting with salt marshes, then a pond where you can admire the birds, a superb viewpoint, followed by a stroll through the village and ending with a walk through the woods.

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kartavan
kartavan

Overall rating : 4.7 / 5

Date of your route : Apr 13, 2025
Reliability of the description : ★★★★★ Very good
Ease of following the route : ★★★★★ Very good
Route interest : ★★★★☆ Good
Very busy route : No

A very beautiful hike through the marshes with lovely views to discover.

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Luis liliane
Luis liliane

Overall rating : 4.3 / 5

Date of your route : Sep 16, 2024
Reliability of the description : ★★★★☆ Good
Ease of following the route : ★★★★☆ Good
Route interest : ★★★★★ Very good
Very busy route : No

The PRs I looked at were fine, sometimes with a little more road and one where the mileage was not quite right, 4 km more. However, this kind of error should be avoided, otherwise overall they were all pretty good. Mer i

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AG
AG

Overall rating : 4.3 / 5

Date of your route : Jul 28, 2024
Reliability of the description : ★★★★☆ Good
Ease of following the route : ★★★★☆ Good
Route interest : ★★★★★ Very good
Very busy route : No

Please note that the passage near the observatory is impassable: barriers indicate that the footbridge is out of service. For how long???

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Anne Françoise
Anne Françoise
• Edited:

Overall rating : 3.7 / 5

Date of your route : Apr 29, 2024
Reliability of the description : ★★★☆☆ Average
Ease of following the route : ★★★☆☆ Average
Route interest : ★★★★★ Very good
Very busy route : No

Hello, we had a little trouble following the description. For example, when it says, "take the path on the right...etc...", it should specify how far away the path is and whether it is the first or second one. We had problems with the salt workers because we took the first path on the right at the start of the hike...

Thank you very much.

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Annie Barguillet
Annie Barguillet

This hike has not yet been completed, thank you for your prompt response, I will keep you informed of any further developments.
I would like to say that I am delighted 🤩 with your app.
I have already used it for other routes.
Have a good evening.

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lessaules7
lessaules7
• Edited:

Overall rating : 4.3 / 5

Date of your route : Sep 21, 2022
Reliability of the description : ★★★★☆ Good
Ease of following the route : ★★★★☆ Good
Route interest : ★★★★★ Very good
Very busy route : No

Very pleasant route.

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francky76320
francky76320

Overall rating : 5 / 5

Date of your route : May 31, 2022
Reliability of the description : ★★★★★ Very good
Ease of following the route : ★★★★★ Very good
Route interest : ★★★★★ Very good
Very busy route : No

A very pleasant short hike that I did twice during my stay in your region.
What I liked most was the tour of the Isle of Rostu, where I was able to observe many species of birds and discover, on the path leading to viewpoint No. 4, some very old pine trees that are worthy of being recognised as remarkable.

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