we decided to take a look at some of the other difficult open-water swims around the UK, starting with a brisk dip north of the border in the Firth of Forth.
Rat Race City to Summit
What it is: A newish point-to-point triathlon that starts outside Edinburgh and finishes with a run to the summit of Britain's highest mountain, Ben Nevis.
Why the swim's tough: The race starts with a 3.8km swim in the Firth of Forth, which flows into the decidedly nippy North Sea. The water at last year's event was a lower-than-expected 9ºC, causing the organisers to shorten the swim leg down to 1km.
Rat Race City to Summit website
What it is: With half, full and double-Iron distances on offer, and all requiring a run up Mount Snowden, this is viewed by many UK triathletes as the country's hardest race.
Why the swim's tough: Cold, long (in the case of the double, very long) yet undeniably scenic late season swim in Snowdonia.
We also rate The Brutal as the toughest ironman distance race in the world
The Brutal website
What it is: Organised by the same people behind Norseman and Swissman, this Iron-distance race sends athletes across some of Scotland's most challenging terrain.
Why the swim's tough: A swim so chilly the distance was shortened in both 2012 and 2013, this Western Highlands epic is one for the hardcore only.
What it is: With a punishing course across the Pembrokeshire countryside that involves a constantly changing gradient, this is seen as one of the hardest IM races going.
Why the swim's tough: Two-laps of choppy sea and a mass of bodies before a long yet memorable run to transition.
We rated Ironman Wales the 4th toughest Ironman distance race in the world
Ironman Wales website
What it is: The 'Perranporth Extreme Surf Triathlon' to give it its full name, this is one of the UK's oldest triathlons and is hosted by the local lifesaving club every year.
Why the swim's tough: The name's a good clue: the race starts with a 1km swim off the rugged Cornish coast, where you'll be glad to be within reach of the local lifesavers.
The Snowman now known as Snowdonia Triathlon
What it is: One of the UK's most iconic races, this takes place in rugged north Wales and includes both Iron distance and sprint events.
Why the swim's tough: Last year saw lots of choppy waves, making the chilly swim in the lake of Llyn Mymbyr even tougher than normal.
Snowdonia Triathlon website
What it is: This new-for-2014 Iron distance event will take place at Hever Castle in Kent this July, looping sections of the existing Gauntlet route and taking athletes on a 140mile journey.
Why the swim's tough: Participants will swim two loops of the Gauntlet swim course along the river Eden, facing strong currents and multiple choke points.
What it is: Taking place in the shadow of Northumberland's mighty Bamburgh Castle, this middle distance race starts with a beach standing start and connects some of the region's best landmarks.
Why the swim's tough: A dip in the North Sea is never one to be taken lightly. Throw in waves and rival triathletes taking your line, and you have a 1.9km battle of mind and body.
Castles Triathlon website
What it is: With a finishing line described by the Guardian as "like a depiction of hell", this monstrously difficult race takes in some of the country's most beautiful scenery.
Why the swim's tough: It takes place in Ullswater, just down the road from Davina's nemesis Windermere, where plenty of shady spots can make the temperature plummet and rumours of giant pike trouble the mind.
Helvellyn Triathlon 2015 – in pics
Helvellyn Triathlon website
Enjoyed this? Check out Iron-distance races: the 7 toughest?
How many of these races have you done? Let us know in the comments below!