Update: Monday 18 September

We hope that you all had a great day out at Swim Serpentine on Saturday!

Below are the latest test results, from tests taken on Saturday morning, showing all four testing sites. We're delighted to confirm that all results were far below the 20,000 'relatively low' threshold.

Update: Friday 15 September

We're looking forward to welcoming you to Swim Serpentine tomorrow!

With thousands of participants set to take part, including 2,000 London Classics hopefuls, it's set to be an amazing day for all.

The forecast is for a beautiful sunny day with temperatures due to peak at 25 degrees so please bring plenty of sunscreen and remember to keep hydrated.

We have more good news! Results from this morning’s tests show the levels of blue-green algae are continuing to decrease.

The detailed results from the four testing locations this morning are:

1. Sample 1 - 10,390 cells/ml
2. Sample 2 - 13,680 cells/ml
3. Sample 3 - 20,690 cells/ml
4. Sample 4 - 16,270 cells/ml

As you can see, three of our four samples are now well below the upper limit of 'relatively low', with one sample at the lower limit of the moderate threshold (and lower than yesterday).

If you've now changed your mind about deferring or requesting a refund, don't worry, just arrive as scheduled for your allocated wave. There’s no need to contact us.

If you have chosen not to swim tomorrow, please submit your request for deferral or refund before 07:00 tomorrow, Saturday 16 September.

We look forward to seeing you all at Swim Serpentine tomorrow!

Update: Thursday 14 September

We are delighted to confirm that we are going ahead with Swim Serpentine on Saturday. 

As we explained in an email to participants earlier today, we have been working hard to reduce the level of blue-green algae to enable Swim Serpentine to take place on Saturday and have been conducting daily testing of the water. 

We’ve just received the results from the water samples we took this morning (Thursday 14 September). Standard testing results measure water quality as excellent and our specialised testing shows blue-green algae levels are continuing to decrease.

The graphic below shows the three standard bands for blue-green algae levels, with indicators showing where our current test results stand and, for context, where the World Triathlon limit results in event cancellation.

The latest results in detail from our four testing locations taken this morning are:

1. 20,910 cells/ml
2. 18,470 cells/ml
3. 22,540 cells/ml
4. 19,080 cells/ml

These levels have been decreasing all week and are deemed safe for swimming by our expert water safety team.

We’ll continue to monitor blue-green algae levels in the Serpentine with further tests tomorrow and will notify you immediately if there is any change to the event going ahead. 

We will also be providing additional measures on the day including extra showers and drinking water for participants.

If you’re still able to join us on Saturday, you don’t need to do anything, and we can’t wait to see you!

However, any participants who are still not comfortable with swimming have been emailed directly with their options.

Update: Wednesday 13 September

We have analysed the latest test results with experts and stakeholders and levels are decreasing. As a result, we are now taking further readings tomorrow morning. We realise this update is later than planned and apologise for this. We will provide a further update by 18:00 tomorrow, however if you are unable to wait for a final decision, you will be able to apply for a refund. Thank you for your patience.

Tuesday 12 September update

As you may be aware, there has been a bloom of blue-green algae in The Serpentine (which is a common occurrence during hot weather).

Swim Serpentine is scheduled to take place on Saturday 16 September, and we have been taking weekly and now daily water samples from the water.

Staff have been doing everything possible to clear the lake and positively water samples are showing a decrease in blue-green algae levels.

Further samples have been taken from multiple areas of The Serpentine today, to enable us to make an informed decision by 17.00 tomorrow (Wednesday 13 September) as to whether the event will go ahead. 

Public safety and comfort is our priority. Should Swim Serpentine not go ahead on Saturday, all entrants will be offered the option of taking part in 2024 (date to be confirmed) or a full refund of the entry fee they paid.

Thank you for your understanding.