Thames Marathon 2021

Sunday 15th August 2021

Event Details

The Thames Marathon is an endurance swim between Henley-on-Thames and Marlow. It covers a beautiful stretch of the Thames and has become one of open water swimming's most prestigious marathon swims. This year we will be offering a choice of two distances:

**Please note that this event has previously been advertised as a 14km event. All registered swimmers have been advised that the distance has been reduced to 10km. You can see the full statement here**


The Thames Half Marathon is a 5.5km endurance swim finishing in Marlow. All swimmers will have the option to either walk/run the approx 5.5-6km from the event HQ in Marlow to the Half Marathon start (this is just for fun, run times will not be recorded) or to be transported by coach for a small additional fee. The swim is split into 3 sections. Swimmers will be required to exit the water at the 2 locks (Hurley at approximate 1.8km and Temple at 3.5km) where drinks and energy snacks will be available.

The Half Marathon swimmer will enter the water between 10.30 and 11.00am, it is anticipated all swimmers will have arrived in Marlow by around 2.00pm. 
Just like the full distance, non-wetsuit places will be limited, but they will not need to be approved. Once the non-wetsuit places are full this will show on the entry system, and only wetsuit places will be available. 

The swim is split into 3 sections. Swimmers will be required to exit the water at the 2 locks (Hurley at 6km and Temple at 8km) where drinks and energy snacks will be available. 

    Wetsuit places (10km)

To apply for a wetsuit place click Enter on the Wetsuit Category below. You will be asked to select your wave, please do so based on the following criteria: We will be setting off small waves at intervals of around 5 minutes starting at 7:00 am.

  • Waves 1, 2, 3 & 4 - these waves are ideal for swimmers who are seeking a faster time and who expect to complete the course in under 3 hours (approximately equivalent to a sub 27 minute mile pace). If you expect your time to be under 2½ hours, please select wave 1, between 2½ and 3 hours select wave 2, 3 or 4.
  • Waves 5-10 - these waves will be mixed ability waves. If you do not consider yourself a racing swimmer, please select one of waves 5 to 10 
    If you wish to swim with a friend or as part of a group, please make sure that you all select the same wave. There will be a cut-off time of four and a half hours, where all swimmers will need to be out of the river. If you anticipate that you will take longer than this, please contact before entering

    Non-wetsuit places (10km)

These places have now all been allocated, please put yourself on the waiting list if you would like to be considered for a non-wetsuit place, should one come available, or apply for a charity place (see below) There are a limited number of places open to non-wetsuit swimmers, subject to experience and ability. This is to minimise the risk to our safety plan. Wetsuits are important for retaining heat and providing buoyancy. If you would like a non-wetsuit place your application will be assessed by the events team for approval. We advise swimmers to be prepared to wear a wetsuit if asked, on the day.

Event Village Update: The event village for both distances will be in Marlow. Parking, registration and bag drop will take place here. Swimmers will be transported by coach to the start of the swim, and will swim back to the event village. There will be no coach back to Henley after the swim.  


We are pleased to be working with SwimTayka as an Official Charity Partner for the event this year.  We have collaborated with them to raise vital funds that will help reduce drowning in underprivileged parts of the world. Sign up for a FREE Charity Place today and pledge to raise £750 / £500 which will allow them to provide free swimming lessons to a much-needed part of the world, to help save lives from drowning and inspire children through swimming.  Each charity place swimmer will receive a fundraising pack and lots more support from the charity.  

Tow Floats will be compulsory for all swimmers, both wetsuit and non-wetsuit for both the 5.5km and 10km distance. There is an opportunity to buy a tow float during the registration process.

Entry Options - Age 18 & over on Sun 15 Aug 2021
Entries closed
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Refund Policy

Please carefully read clause 5 (cancellation by you) and clause 6 (cancellation by the organisers) of our terms and conditions

Sun 15 Aug 2021 at 07:00
Contact Info
Henley Swim
01491 577922
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