A dam with a sluice is created across a suitable tidal inlet, or a section of river estuary is made into a reservoir. As the tide comes in, it enters the mill pond through a one way gate, and this gate closes automatically when the tide begins to fall. When the tide is low enough, the stored water can be released to turn a water wheel.
Tide mills are usually situated in river estuaries, away from the effects of waves but close enough to the sea to have a reasonable tidal range. These mills have existed since the Middle Ages, and some may go back to the Roman period.
Possibly the earliest tide mill was located in London on the River Fleet, dating back to Roman times. The earliest excavated tide mill, dating from 787, is the Nendrum Monastery mill on an island in Strangford Lough in Northern Ireland. Its millstones are 830mm in diameter and the horizontal wheel is estimated to have developed 7/8HP at its peak. Remains of an earlier mill dated at 619 were also found.
The earliest recorded tide mill in England was in Dover harbour, mentioned in the Domesday book (1086), as were the mills on the Lea River at Three Mills Island, now in London's docklands, which by the 18th Century had become the largest in England. There were many tide mills in London, including two on London Bridge.
Woodbridge Tide Mill, an excellent example, survives at Woodbridge, Suffolk, England. This mill, dating from 1170 and reconstructed in 1792, has been preserved and is open to the public. Its water wheel can be seen turning. The only working tide mill in the United Kingdom is Eling Tide Mill in Eling, Hampshire. Another example, now only visible in historic documents, is the mill in the hamlet of Tide Mills, East Sussex.
At one time there were 750 tide mills operating along the shores of the Atlantic Ocean. Approximately 300 in North America, 200 in the British Isles, and 100 in France. The Rance estuary in France was also home to some of these mills.