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 Saltstraumen maelstrom, or an underwater obstruction (a reef or rising seabed), such as is found at the Portland Race.
In extreme cases, such as Skookumchuck Narrows in British Columbia, through which tides can travel at more than 17 knots, very large whirlpools develop, which can be extremely hazardous to navigation.
Notable tidal races
- Cape Reinga in New Zealand
- Skookumchuck Narrows in British Columbia, Canada
- The Bitches in Wales, United Kingdom
- Falls of Lora in Scotland, United Kingdom
- Portland Bill on the Isle of Portland, United Kingdom
- The Alderney Race (12 knots+) on Alderney
- Horizontal Falls in Western Australia, Australia
- Naruto Strait between Shikoku and Awaji Islands, Japan
- Reversing Falls in Saint John, New Brunswick, Canada
- Gut (coastal geography) – A narrow coastal body of water, a channel or strait, usually one that is subject to strong tidal currents, or a small creek
- Rip current – Narrow current of water which moves directly away from the shore, cutting through the lines of breaking waves
- Tidal bore – A water wave traveling upstream a river or narrow bay due to incoming tide