Barrage d'Arzal

Barrage d'Arzal is a dam and lock system spanning the Vilaine River with five sluice gates and three dedicated fish passages for managing water flow. The installation distributes drinking water to more than one million residents across multiple regions through its treatment facilities.

Planning for this facility began in the 1930s following devastating floods that threatened the region and its residents. World War II interrupted the project, which was not completed until 1970.

The dam reshaped daily life along the Vilaine, requiring fishermen and boaters to adapt their routes and practices as water levels and flows changed throughout the estuary.

The best viewing happens at moderate water levels when you can observe the sluices and passages working. The site is accessible on foot from Arzal and does not require special equipment to approach the structure.

The structure slowly settles, sinking about half a meter every decade because it rests on 30 meters of silt. This gradual subsidence requires regular height adjustments to maintain its functioning.