Concerned about preserving the Rance ecosystem, Electricité de France operates the tidal power facility so as to limit its impact on the environment. Regardless of the constraints of the power network, Electricité de France always endeavours to adjust the high and low tidal level of the reservoir according to the movement of the tides so as not to disturb the biological balance of the aquatic environment.
Research carried out in 1995 by a research laboratory of the National Museum of Natural History showed that the Rance estuary has a rich and varied aquatic, namely benthic life. Furthermore, although the construction of the dam modified the currents in the estuary and, consequently, the geographical distribution of the sediments, the studies available on the sedimentary balance seem to point to a natural evolution. To further enhance its role in favour of the environment, Electricité de France takes part as a user in the Operation Committee of elected representatives and users of the Rance (Coeur) entrusted with defining and financing projects to preserve the estuary. In 1995, the partners decided to devote three million French francs to studies and experimentation prior to the signing of the next Rance Bay contract which will concern the quality of water, navigability, banks and marine farms of the estuary. Electricité de France devoted 600,000 French francs to this amount