Fast-moving tidal flow passing through a constriction, forming waves, eddies and strong currents
Tidal race or tidal rapid is a natural occurrence whereby a fast-moving tide passes through a constriction, resulting in the formation of waves, eddies and hazardous currents. The constriction can be a passage where the sides narrow, for example the Gulf of Corryvreckan and the Saltstraumenmaelstrom, or an underwater obstruction (a reef or rising seabed), such as is found at the Portland Race in the United Kingdom.