Sixty years have passed since the Rance tidal power plant began operation, and it is now showing signs of long-term environmental impact. Located between the towns of Saint-Malo and Dinard in Brittany, France, the plant was the world's largest tidal power facility from 1966 until 2011. It was originally designed to harness the power of the tides to generate electricity, but its presence has also altered the natural dynamics of the Rance estuary. One of the most significant changes is the buildup of sediment, or silt, in the estuary. Monitoring has shown that the seabed has thickened over time due to reduced tidal movement, which used to naturally clean the area. The Rance barrage, which spans 750 meters across the estuary, has dampened the natural rise and fall of the tides. As a result, the estuary has become more stagnant, leading to silt accumulation of several meters since the 1980s. This has transformed the ecosystem, with some species disappearing and others returning. The ecological changes are evident in the local wildlife. Lamprey and eel, which once thrived in the estuary, have largely disappeared. In contrast, species like sea bass and flounder are now more common, likely because they are smaller and faster, able to navigate through the barrage's turbines. The shift in species highlights the impact of the barrage on the hydrological and sedimentary balance of the area. Efforts are now underway to manage the sediment buildup and find sustainable ways to operate the plant without compromising its energy output. Since 2018, an Experimental Sediment Management Plan has been in place, involving regular bathymetric surveys to track silt accumulation. Recent data shows a one-third decrease in sediment volume since 2018, which may be linked to recent operational adjustments at the plant. EDF, the company that operates the facility, has invested over 13 million euros in sediment management since the 1990s, and a new management plan is currently in effect through 2028. Starting in 2026, new operational models will be tested to reduce silt deposits while maintaining energy production, ensuring the plant continues to serve the region sustainably.