Three technologies are used to capture the energy from tides: tidal dams, tidal fences and tidal turbines. All three generate electricity in the same way that a dam does.

A tidal dam is built across a bay or estuary. As the tide rises and falls, a gate is opened, causing water to flow through a turbine connected to an electric generator. Electricity can be generated by water flowing both into and out of the bay.

The energy-producing potential of a tidal dam depends on the difference in ocean level between high and low tides. The greater the difference, the more electricity that can be produced. To be practical for electricity generation, the difference between high and low tides must be a least 15 feet. Only about 40 sites on Earth have tides that high. The Bay of Fundy between Nova Scotia and New Brunswick in Atlantic Canada has the highest, with a difference of 17 meters (55 feet).