CHALLENGE,  Event reviews

Marathon Swims – 10km in the pool

Simon Griffiths describes Marathon Swims as a challenging but fun way to swim 10km, with an option to raise funds for good causes.

In 2008, open water swimming was introduced to the Olympics. The 10k race takes top swimmers a little under 2 hours – slightly quicker than top runners can complete 26.2 miles on the road. The distance is therefore often considered to the swimming equivalent of a marathon. While mass participation open water 10km swims are popular, until the creation of Marathon Swims in 2017, there was no opportunity for regular swimmers to challenge themselves to the marathon distance in the pool.

In a 50m pool, you need to swim 200 lengths to complete 10km. You could put your head down and plough up and down a lane for several hours, but most people would find that dull. In addition, you could get stuck in a lane with people of different speeds and abilities, with the risk of argument that brings. Luckily, Marathon Swims has derived a swim format that reduces this issues and turns the distance into a fun and achievable challenge for most swimmers.

Here’s how it works. Starting in the bottom right hand corner of the pool, you swim two lengths in lane 1, always keeping to the right. At the end of the second length, duck under the lane rope and do the same thing in lane 2. Repeat until you’ve done two lengths in each lane, bringing you to the bottom left end of the pool, for a total of 20 lengths or 1km. Exit the pool, walk or jog back to the start and repeat nine more times.


I admit, I was sceptical before I tried it. My previous long-distance swims were in open water, usually with stunning and varied scenery, and with plenty of space either side of me. The idea of doing 10 x 1km in a pool was therefore not appealing. The lane changing struck me as an unnecessary complication and the getting-out-and-running-back-to-the-start as plain wrong.

But having done it, I’ve revised my opinion. The formula works well. Firstly, traversing across the pool with each 100m gives you a clear and motivational visual marker of your progress, with the bonus that there is no need to count lengths. Secondly, rather than being stuck in a lane with the same people for several hours and risk conflict by repeatedly overtaking or being overtaken by the same people, you rarely encounter anyone more than once or twice. Thirdly, exiting the water after each kilometre is a good chance to stretch your legs, grab something to eat and check your progress on the live reporting screens.

Mostly I could swim undisturbed at my own pace. When I needed to overtake, there was usually plenty of space to pass safely. The only delays were when I was temporarily stuck behind one swimmer trying to overtake another and a couple of times in the “no-overtake” zone, the last 5m of each 100m lap. I’ve experienced much worse in public swimming sessions.

The event grew quickly in its first three years but then like much else was forced to cancel because of the covid pandemic. 2022 is its first year back. Back in 2019, Oliver Wilkinson became the first person to break the 2:20 barrier with a sharp 2:19:49 swim, while previous female record holder Hayley Moore beat her own time by three minutes to finish first woman in 2:25:03. In total, 233 people completed the 10km. The median time was just under four hours and the longest was a determined 8:14.22. Marathon Swims has clearly attracted a wide range of swimmers. There are also options for 1km, 5km and team 10km challenges.

Despite some fast times at the front end, Marathon Swims is more of a challenge than a race and there is an informal code of conduct that asks swimmers to be kind to each other. Given that some of the people in the water are novice swimmers and possibly nervous, it’s only fair to ask faster, more confident swimmers to be mindful when overtaking.

For regular long-distance open water swimmers, Marathon Swims offers an opportunity to check your speed and fitness. Think of it as a warm, early winter benchmark training swim to see where you are after a summer outdoors. If you’re new to outdoor swimming and thinking of trying out some longer open water swims in the future, this is a good opportunity to see how you cope with the distance and experiment with nutrition.

Standard tickets for the 2022 event are sold out but it’s still possible to get an entry through one of the charity places with Level Water. Check the Marathon Swims website for details.

In addition, there is a Marathon Swims Virtual Challenge running through November.


Event details

View event listing on Outdoorswimmer.com

Name: Marathon Swims

Location: London Aquatic Centre

Distances: 1km, 5km, 10km and 10km team

Water type: Pool

Wetsuits: Not allowed.

Next event: 12 November 2022

I created Outdoor Swimmer in 2011 (initially as H2Open Magazine) as an outlet for my passion for swimming outdoors. I've been a swimmer and outdoor swimmer for as long as I remember. Swimming has made a huge difference to my life and I want to share its joys and benefits with as many people as possible. I am also the author of Swim Wild & Free: A Practical Guide to Swimming Outdoors 365 a Year.