On 16 June 2006, the French prime minister and regional authorities announced a €164 million project (Projet Mont-Saint-Michel) to build a hydraulic dam using the waters of the river Couesnon and of tides to help remove the accumulated silt deposited by the rising tides, and to make Mont-Saint-Michel an island again. It was projected to be completed by 2015.
The construction of the dam began in 2009 and is now complete. The project also included the destruction of the causeway and its visitors car-park. It will be replaced by a light bridge, allowing the waters to flow freely around the island, which will improve the efficiency of the now operational dam, and a replacement car-park on the mainland. Visitors will use small shuttles to cross the future bridge which will still be open to pedestrians and unmotorised vehicles.
excerpt from http://en.wikipedia.org/wiki/Mont_Saint-Michel