Corryvreckan (Scotland, but still) has one of the fiercest tidal races in the world - the story goes that George Orwell almost drowned in one of the whirlpools.

Corryvreckan (Scotland, but still) has one of the fiercest tidal races in the world - the story goes that George Orwell almost drowned in one of the whirlpools. 'Although not, as is sometimes believed, formally classified by the Royal Navy as unnavigable, the nearby Grey Dogs, or Little Corryvreckan, are classified as such.[1] The Admiralty's West Coast of Scotland Pilot guide to inshore waters calls it "very violent and dangerous" and says "no vessel should then attempt this passage without local knowledge". Experienced scuba divers who have explored the waters have described it as "potentially the most dangerous dive in Britain"' https://en.wikipedia.org/wiki/Gulf_of_Corryvreckan https://en.wikipedia.org/wiki/Gulf_of_Corryvreckan