Tidal energy: this dam, the Rance barrage, is situated at a unique location where the tidal range at equinoxes reaches 13.5 metres. It is 750 metres long and creates an artificial lake of 22 square kilometres. As the tide rises water is allowed to enter the lake in the river estuary, and as the tide falls it is passed through turbines to generate electricity. The barrage, which carries a major road, has been operating at the Usine Maremotrice at La Rance in northern France since 1966.