Perte du Rhône

The Perte du Rhône is a narrow limestone slot canyon located between Ain and Haute-Savoie departments, where water once forced through nearly vertical walls. Today the original canyon lies submerged beneath a reservoir system created by dam construction upstream.

The canyon was carved over millennia by the Rhône River eroding through limestone bedrock to create its distinctive narrow passage. The construction of a dam in the mid-20th century flooded the original formation and completely altered this natural landmark.

The name refers to the river's disappearance into the canyon, a phenomenon that locals historically observed during dry periods. This geological feature became part of how residents understood the boundary and character of their region.

The best time to visit is after rainfall or when water levels are high, as geological features become more visible. Since the area is now a water reservoir, visitors should explore from the shoreline and look for marked access points.

Scientists explored the area in the 1800s and documented fossils embedded in the limestone layers that revealed the region's deep past. These paleontological discoveries attracted researchers and demonstrated how much geological history was written into the stone itself.