Tidal power generates electricity in similar fashion to hydroelectric power. A dam-like structure is constructed across an estuary to trap a high tide of water and then let it pass through turbines to generate electricity. The water flow can generate electricity on the falling tide only, or on the falling and rising tide. The Rance Estuary in Brittany (France) is an example of a successful tidal plant. The UK has the potential to widely use tidal power with the Severn and Mersey estuaries being possible sites.