National Id
Site name
Black Marsh
Since 1984, the Hunting Federation of Ille-et-Vilaine Department has been rehabilitating a 550-hectare marshland that was heavily developed in the last century. Rehabilitation began with the replacement of corn crops by hay and pasture natural meadows via contractual agreement (with finacing) with the farmers. It continued with the restoration of a peat bog and a reed bed. In addition, due to the highly developed nature of the marsh and its drainage by a highly recalibrated and deepen watercourse, artificial water level management was also put in place to allow winter flooding. The project's objective is to improve the marsh to allow migratory waterbirds halting and to improve some of the marsh functionalities (carbon sequestration by peat and natural water purification). They have been achieved with regard to bird halting, but water level management is not currently optimised and will be reviewed to improve the hydrological functioning of the marsh.
Reviewed by
Light or indepth?
The in-depth description of the case study
Location description
Included in the vast Dol marshes (10,500 ha), the Châteauneuf marsh is a regularly flooded depression made up of peaty alluvium and juxtaposing the Mont-Saint-Michel bay. Until 1950, it included one residual lake (the Mare de St-Coulban), before it was dried out. The marsh has since been drained by the Meleuc river, which shows a strong recalibration. Before the project, the marsh was subject to an intensive agricultural use, mainly for corn. It included a former peat bog that had been mined and drained.
RBD code
FRG-La Loire, les cours d'eau côtiers vendéens et bretons
Climate zone
cool temperate moist
Mean annual rainfall
600 - 900 mm
Mean rainfall unit
Monitoring parameters
Piezometric monitoring:
20 piezometers have been installed and monitored monthly since 2016.
Physico-chemical monitoring:
A physico-chemical probe is installed on the marsh and measures water transparency, conductivity, dissolved oxygen, water pH, water height and silt depth.
Ecological monitoring:
A monitoring of amphibians, reptiles (laying 80 herpetological plates), fish and aquatic invertebrates was carried out. The Large Marsh Grasshopper population has been monitored since 2019.
The floral procession evolution is monitored in oligotrophic and peaty areas by applying a National Museum of Natural History methodology to record the communities evolution.
Bird counts have been carried out by the Hunting Federation of Ille-et-Vilaine Department for 30 years. Since 2016, they have been supplemented by a winter waterbird count, a monitoring of the reedbed passerines, ardeidae and anatidae reproduction. A mapping of the singing passerines is also carried out.
Biophysical impact assessement method
Piezometric, physico chemical and ecological monitoring before and after the application.
Project scale
Project scale specification
Marshland area (370 ha)
Installation date
Area (ha)
370 ha
Favourable preconditions
The deployed NWRMs were selected in the first place because they allowed the creation of habitats favorable to biodiversity and waterfowl parking.
However, the complete restoration of the hydrological functioning of the marsh has not been completed. The NWRMs therefore need to be complemented by water level management by means of a valve.
Design contractual arrangement
Arrangement type Responsibility Role Comments Name
Design consultation activity
Activity stage Key issues Name Comments
Design land use change
Land use change type
Design authority
Authority type Role Responsibility Name Comments
Others (please specify in column H)
Initiation of the measure
Hunting Federation of Ille-et-Vilaine Department
Key lessons
(See p 5 of the document, in French) Overall and after 35 years of effort, the marsh has become again a waterbird halting with EU importance in the Miont-Saint-Michel bay. A lot of invertebrates are present while the typical plant community of a peat bog is hindered by the water level management still to be improved. The hunting federation would want to increase the water levels in summer to avoid peat mineralisation but the farmers who are growing maize are against.
Success factor(s)
Success factor type Success factor role Comments
Financing possibilities
main factor

The low land pressure (and therefore low price) on these lands has facilitated acquisitions by the Hunting Federation of Ille-et-Vilaine Department. As they are not traditionally associated with nature protection in the eyes of the general public, the project was also an opportunity to bring about a change of perspective.

Financing type Comments
Barrier type Barrier role Comments
Attitude of relevant stakeholders
main barrier
It has been difficult to make elected officials, the SAGE (water development and management scheme), as well as farmers who are still growing maize, understand the importance of restoring the wetland's functionality.
Driver type Driver role Comments
Financing share
Financing share type Share Comments
Policy description
The Châteauneuf marsh belongs to the complex of peripheral wetlands of the Bay of Mont-Saint-Michel, and as such plays a role in welcoming birds, especially during migration and winter. It is thus a migratory stage for the Aquatic Warbler, a passerine species classified as "vulnerable" on a global scale by IUCN and also the most threatened in Europe. The interest of the site also concerns other faunal groups as well as the flora, hosting some species that are uncommon or rare on the scale of Brittany.
It is the most massive peat deposit in the region.
The pressures on the site result from its development in the middle of the last century to facilitate agricultural activities:
Corn monoculture;
Hydrological dysfunction causing the marsh to dry up in both winter and summer, and promoting peat mineralization.
Restore wet habitats, especially peat meadows;
Improve the marsh's carrying capacity for biodiversity, and in particular birdlife;
Improve the regulatory role of the marsh (carbon sequestration in peat, natural water purification);
Allow educational and recreational uses;
Enhance the value of the Hunting Federation of Ille-et-Vilaine Department action on the management of sensitive heritage habitats;
Collaborate with agricultural stakeholders.
Policy target
Target purpose
Policy pressure
Pressure directive Relevant pressure
Policy area
Policy area type Policy area focus Name Comments
Policy impact
Impact directive Relevant impact
Policy wider plan
Wider plan type Wider plan focus Name Comments
Environment & Biodiversity
wetlands of the Bay of Mont-Saint-Michel
Policy requirement directive
Requirement directive Specification
Information on Ecosystem improved biodiversity
The monitorings carried out have shown that:
An increase in waterbirds halting;
An increase in breeding passerines;
An evolution of the common flora towards a more specific procession of peaty environment flora;
An increase in the geographical distribution of the Large Marsh Grasshopper.
The restoration of the reedbed has allowed the installation of the Marsh Warbler, which has only a few nests in Bretagne.
Information on Water quality overall improvements
A visual observation of the area allowed the Departmental Hunting Federation to observe a decrease in eutrophication in the canals
Information on Mitigation other biophysical impacts
Piezometric monitoring confirmed that the marsh dries out in the summer following the opening of the gates. The water levels obtained are too low to preserve the peat, and expose it to mineralization.