The connection between the Mont Saint-Michel and the mainland has changed over the centuries. Previously connected by a tidal causeway uncovered only at low tide, this was converted into a raised causeway in 1879, preventing the tide from scouring the silt around the mount. The coastal flats have also been polderised to create pastureland, decreasing the distance between the shore and the island, and the Couesnon River has been canalised, reducing the dispersion of the flow of water. These factors all encouraged silting-up of the bay.