What kind of actions for the Lac au Duc?

Since the end of the 1980s, the development of cyanobacteria in Lac au Duc has become a problem, which is increasing every year and resulting in bathing and consumption bans. Since the 90s, several temporary actions have been put in place to fight against these cyanobacteria but without definitive results. In response to these concerns, on June 4, 2018, the Community Council approved Ploërmel Community's participation in the international InterregCPES project (see Context of the Action) to provide a thorough understanding of the Lake's functioning.

Context of the action

Lac au Duc and the Yvel-Hyvet catchment area is one of ​​6 pilot sites of the EU Interreg prject - Channel Payments for Ecosystem Services (CPES). In this case study, the scientific partners (CNRS, INRA, University of Rennes 1, Sara Hernandez Consulting, West Agrocampus, CRESEB) and local partners (Great Basin of the Oust, Ploërmel Community, Pays de Ploërmel) seek to restore the quality of the water and the environment. They are doing this by studying the fluxes of phosphorus in the watershed, the financial mechanisms for PES, changes in farming practice, the dynamics of development of the cyanobacteria in the Lake and actions curative in Lake swimming area. For Lac au Duc and the Yvel-Hyvet catchment area, the project partners are investing more than 1.5 million euros for the territory.


  •  Inform about the fragility of Lac au Duc and the rivers, the water resource and the recovery of the aquatic environment.
  •  Highlight the complexity and richness of phytoplankton biological life as well as the variability of developments and the difficulty of anticipating plankton blooms of cyanobacteria.
  •  To bring out the societal demand.

Useful information

    Date: Friday, June 7, 2019 from 8pm
    Venue: Room A, Festival Hall Ploërmel


  •     8:00 pm: Introduction

  • 20h15: Introduction of phytoplankton and cyanobacteria - University of Rennes 1

    • Public Health Risk Management-ARS 56

    • Impact on economic structures-Fishing, Nautical Club, AEP

    • Remediation actions - University of Rennes 1

  •     9:30 pm: Questions / Answers

  •     22:00: Friendly pot