Completing any open-water swimming event is a huge and ultimately rewarding challenge, with often cold waters, currents, waves and more often encountered on the way to finishing pontoon success and that celebratory warming cup of tea.
Not all swim events are created equal, however, with many upping the ante for vastly experienced open-water swimmers to test their endurance capabilities in deep, bracing and unpredictable waters.
It's therefore important that you have trained appropriately for the event, have the right kit and are aware of (and can recognise) the signs of cold water shock.
Here are qualified swim coach and 220 Triathlon editor Helen Webster’s toughest UK contenders, starting with a couple of monster options from country to country…
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Toughest open-water swimming events in the UK
Lake District Triple Crown
Cumbria, England
23.75 miles
Coniston. Ullswater. Windermere. Home of gentle boat rides and family days out, of course, but these vast lakes also host plenty of open-water swimming events. And the 23.75-mile Chillswim Triple Crown is the mother of all Lakeland swim challenges, awarded to entrants who complete an end-to-end swim of all three lakes in the same year.
The distances (5.25 miles in Coniston on 21 June; 7.5 miles in Ullswater on 12 July; 11 miles in Windermere on 6 Sept) are enough to make many swimmers’ toes curl, but what makes them so testing is the unpredictable nature of the weather and water conditions in each lake. Although it’s the middle distance of the three, swimmers often report that the 7.5 miles in Ullswater is the toughest due to its crosswinds and bracing waters (around 14°C in July).
The Gwineas
Gorran Haven, Cornwall
2.4 miles
Organised by a company called the ‘Mad Hatters’, there are no prizes for guessing a certain type of madness identifies these events. So, what’s the Gwineas? Put simply, it’s a coastal swim event in Gorran Haven, near Mevagissey in Cornwall, which takes you 1.2 miles straight out to sea, around a tiny rocky island that gives the event its name and then 1.2 miles back in. Sounds simple, right? Not so much….
Conditions here are so varied that in the first year only 15 of the 120 competitors made it around the rock in choppy seas and 94 were rescued by the safety team. Another year mist and fog made navigation tricky, 2023 and 2024 saw most competitors finish, while 2024’s event had to be cancelled for safety. Will 2025 be a good year? We’ll find out on 15 June.
The Menai Strait
Y Felinhelli, Wales
16 miles
Taking the award for toughest Welsh swim is the Menai Strait. This 16-mile-long sea channel separates the island of Anglesey from mainland Wales, with a central region known as the ‘Swellies’, a unique environment with strong, reversing tidal flows (sometimes reaching speeds of four metres per second), rapid currents and swirling whirlpools.
The Strait also has many small, offshore islands, and rocks close to the surface of the water that need to be navigated.
Loveswimrun offer a 6.5km or 2.5km guided swim for experienced swimmers – and warn swimmers not to try and go it alone!
The Channel/North Channel Swim
Dover to Calais; Northern Ireland to Scotland
21 miles
Want to complete a nation-to-nation swim? Then you can take your pic from swimming the English Channel (strictly speaking it’s not all in the UK) or from Northern Ireland to Scotland. Ticking off 21 miles from Dover, England, to Cap Gris Nez near Calais in France, the Channel Swim is the stuff that swim dreams (or nightmares) are made of.
The Dover Strait is renowned for having strong tidal flows with a large rise and fall in water from high to low tide, plus you’ll likely endure cool water (15°C in June to 18°C in September), changeable weather, waves and one of the world’s busiest shipping lanes. A pilot boat is essential, as is plenty of training, but you can also swim the channel as a relay team.
If that’s whetted your appetite for more ultra swim fun, there’s also the 21.4-mile North Channel Swim, which typically starts near Donaghadee on Northern Ireland's Ards Peninsula and finishes on Scotland's Rhins of Galloway.
The Gulf of Corryvreckan
Gulf of Corryvreckan, Scotland
0.75 miles
Taking our toughest swim trophy in Scotland is the Gulf of Corryvreckan. It’s the shortest swim in this list at only 1,200 metres (0.75 miles), taking you between the Inner Hebridean islands of Jura and Scarba. What makes it unique is that it’s the third largest whirlpool in the world… flood tides and outflow can create waves of more than nine metres and legend has it that you can hear the roar of the water from 10 miles away!
So why are we suggesting anyone swim here? Well, there are limited times on certain slack tides each month when the water is calm enough to swim across. Always choose an experienced guide though – swim trip operator Swim Trek include the Gulf of Corryvreckan in some of its itineraries.
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Main image: swimmers in an event/Getty
