THAMES MARATHON

Long-distance swimming marathon from Henley-on-Thames to Marlow

SUNDAY 9th AUGUST 2026

When and Where:
Sunday 9th August 2026
From 7.00am
Marlow

Distance*:
Half Marathon 5.5km
Mid-Distance 9km
Full Marathon 13km
All distances approximate
All downstream

Entry Fee:
From £30

Information:
Minimum age 18
Tow floats compulsory

Racecheck Gold Award

The Thames Marathon is an award‑winning endurance swim between Henley‑on‑Thames and Marlow, with a choice of three distances to suit different goals and experience levels. It takes in one of the most beautiful stretches of the River Thames and has become one of open water swimming’s most respected and sought‑after marathon swims. All distances follow the river downstream.

The Event Village will be based in Marlow. Swimmers will travel by coach to the start of their chosen distance — full, mid, or half — before swimming back to Marlow to finish together and enjoy the atmosphere at the riverside. There’s also the option to walk or run to the start of the half‑marathon .

THAMES MARATHON
Approx 13km

The 13km distance is divided into four sections. Swimmers will leave the water at Hambleden, Hurley and Temple Locks, where drinks and snacks will be available before re‑entering the river.

HALF MARATHON
Approx 5.5km

MID-DISTANCE
Approx 9km

The 5.5km and 9km distances are split into three sections, with swimmers exiting at Hurley and Temple Locks for refreshments and a short break before continuing downstream.

We are really happy to be working the charity Level Water in 2026. Level Water gives children with disabilities the opportunity to learn to swim, and believes that from physical development to social and emotional confidence, swimming is a vehicle to change lives for the better. To create long-lasting impact and make this happen, the charity unites and collaborates with teachers, families, fundraisers, pools, supporters, governing bodies and children with disabilities, helping the whole industry to share their mission.

Charity places at the Thames Marathon are available from £30, plus a pledge to fundraise a minimum amount for Level Water to help with their incredible work. Please use the button below to see the distance options, costs and fundraising targets.

long-distance swim | The Thames Marathon
long-distance swim | The Thames Marathon
Where does the swim start and finish?

The event village will be in Marlow.

The Thames Half Marathon 5.5km will start above Hurley. The start will only be accessible to swimmers or walkers, there will be no vehicle access to the start (disabled swimmers please contact enquiries@henleyswim.com to discuss options).
The Thames Marathon Mid-Distance will start at Hambleden Lock. Coaches will drop swimmers at the start.

The Thames Marathon Full-Distance swim will start in Henley. Coaches will drop swimmers to the start.
All distances finish at Higginson Park, Marlow. All swims are downstream.

Where should I park for the event?

There are plenty of public car parks in Marlow operating pay and display. We will transport swimmers by coach to the swim start, and they will be able to walk back to their cars after completing their swim.

We encourage swimmers to car share wherever possible. If you are looking for a lift or would like to offer space in your car, please post on Henley Swim Chatter, our Facebook group.

Will there be bagdrop?

There will be a bag drop facility in Marlow. We will tag your bag for identification purposes, and you will need to show your numbered hat to be able to collect your bag after your swim.

Can I swim in a team with a group of friends?

Absolutely, in fact we encourage it. The more people who swim together and look out for each other, the safer the event is. If you wish to swim with friends, please make sure that you all enter the same wave.

Will I be able to wear a tow float?

All swimmers will be required to use a tow float and are advised to get used to swimming with one before the event.

How will you ensure that those who want to do solo swims are able to do so safely?

We have a fully approved safety plan that ensures coverage across the full course throughout the event. In addition ALL swimmers will be required to use a tow-float.

Can I swim non-wetsuit?

Swimmers that enter the 5.5km event have the choice of wearing a wetsuit, and will be asked on the registration form. We have a limited number of non-wetsuit places available for both the 9km and 13km distances. This is to minimise the risk and to adhere to our safety plan. Wetsuits are important for retaining heat and providing buoyancy. If you would like a non-wetsuit place in the 9km or 13km distance, you will be asked some questions during the registration process. You may be asked to supply more information to the organisers to qualify for a non-wetsuit place.

Non-wetsuit places sell out very quickly, we recommend applying as soon as registration opens.

How many feed stops will there be ?

There will be 3 feed stops for the full Thames Marathon and 2 for the Mid-Distance and Half Marathon.

What food will be available at the feed stops?

We will provide a bit of everything for this long-distance swim, including bananas, energy bars, energy drinks, water, some chocolate, sweets, and some salty snacks. If you wish to use energy gel, please bring your own in your tow float, so that you know the particular brand that you use will suit you.

How will the start work (full marathon)?

The slower swimmers will set off first. The faster swimmers will set off after with those expecting to finish under 3 and a half hours setting off last. Swimmers will be dropped at the start ‘swim-ready’ and will get off the coach, walk to the start and straight into the water for a rolling start within their wave time.

How should I choose which wave to enter?

The Thames Marathon will be setting off from Henley from 7.30am.  Strong swimmers who are seeking a faster time and who expect to complete the course in under 4 hours (approximately equivalent to a sub 27-minute mile pace) should select waves 7-10. If you expect your time to be under 3½ hours, please select wave 10, between 3½ and 4 hours select wave 7, 8 or 9. Other swimmers should select wave 1 – 6 – these are all mixed ability waves. If you wish to swim with a group, please ensure that you all select the same wave.

Are there cut-off times?

There will be a cut-off time of six and a half hours for the full marathon, 5 hours for the mid-distance marathon and three and a half hours for the half marathon, where all swimmers will need to be out of the river. Remember all swims are downstream. If you anticipate that you will take longer than this, please contact enquiries@henleyswim.com before entering.

Are there toilets on the course?

There are toilets at Higginson Park. There are a couple of cafes and pubs near the walking route. Please note that once you have left Higginson Park on the coach, there will be no toilets at the start of either the full, 9km or half-marathon.

Can supporters walk the route?

The route is walkable, by following The Thames Path. It is also possible to cycle the route, although there are a large number of kissing style gates where you may have to lift your bikes to get through and it may be difficult with tag-alongs.

Please note that there is still a diversion in place on the Thames Path, due to the footbridge at Temple Lock being closed. More details…

Supporters that start with their swimmer at Higginson Park can walk upstream as far as Temple Lock, and then walk back downstream alongside their swimmer. Alternatively they can stay at the event village or go into Marlow for a coffee, and wait for the swimmers to return.

Supporters can be dropped at the start of the full-distance in Henley by friends or family with their swimmer, and walk the full distance of the course. There is public parking available in Henley Town Centre near to the start of the swim, but spectators and swimmers would have to make their own way back to their cars after the swim.

Can I talk to fellow swimmers in advance of the event?

Definitely, we have set up Henley Swim Chatter as a facebook forum, where you are able to discuss anything with fellow swimmers from nutrition and training tips to transport to the event on the day.

*A Note About the Distance
The actual distance that you swim will depend upon several factors including the start and finish points, the precise course (inside or outside of the bends), how straight you swim (zig zagging even slightly can make a difference across this distance) and the exact location of the exits and re-entries around the locks and weirs. Some of these variables will not be confirmed until much closer to the event.
On average the distance travelled will be around 5.5km, 9km or 13km however this is not ratified.