Once again the quality of the water in the River Thames and rivers UK-wide is under scrutiny and frequently in the media. As lovers of open water swimming and believers in the benefits it brings to both physical and mental health, we fully support local and national initiatives to protect the UK’s oceans, lakes and rivers. We agree that pollution is a problem and thank those that are bringing it to the forefront of important discussions about the future health of our waterways.
We have been testing the water quality in our stretch of the Thames several times a year, for many years, between June and August. The water is tested for E.coli and Intestinal Enterococci and measured against the Environment Agency Guidance for Bathing Water Quality. We test the week prior to our first event of the season, and then on the day of each of our events. Since 2019 86% of the results have come back as Excellent, and 93% as Good or Excellent.
All indicators point to the fact that the water quality after heavy rainfall is likely to be worse. The Met Office has confirmed that April 2024 has been the sixth wettest on record, and the UK has already seen 96% of its average springtime rainfall in just two of the three spring months. It is therefore no surprise that discharges have been more frequent at the start of 2024. We expect the water quality in summer, when our events take place, to be better. After heavy rainfall, water treatment facilities can’t cope with the extra water and a ‘storm discharge’ happens where water from the plant is released into our waterways. This ‘storm discharge’ is likely to be a mix of untreated sewage and rainwater. While we can see from the Thames Water live Storm Discharge Map where and for how long discharges happen, (through their EDM – Event Duration Monitoring system) there is no way for us to tell how diluted this mix is when it is released, and if it is coming out as a trickle or a gush.
Thames Water themselves have said the monitoring has limitations: ‘Although EDM gives us valuable insight to how our storm overflows are working, it isn’t always accurate. The monitors are sensitive and can play up. Even the movement of a weed growing in front of the monitor could set it off, indicating that the overflow is active when it isn’t. So when a monitor triggers, we can’t say that a certain section of the watercourse definitely contains sewage, or promise that it’s safe to swim in.’
There is also evidence to suggest that poor quality water moves on quickly in the river environment. In tests that River Action conducted in Henley every weekday over a 4-week period from 30th May to 27th June last summer, they confirmed that in most cases in their month of testing ‘the results for e-coli and intestinal enterococci were at levels that would result in a bathing water status as ‘good’ for e-coli’ and ‘excellent’ for intestinal enterococci.’ They recorded high levels of bacteria on one day on 20th June, which ‘reduced within 24 hours and returned to ‘satisfactory’ bathing status levels by 48 hours.’ It is important to be aware that some recent press articles have been based on water quality test results that have been taken shortly after a storm discharge.
Open water swimming by its nature, carries a certain level of risk, in that swimmers are interacting with natural and ever-changing environments where factors such as currents, weather and water quality are not always predictable, and swimmers will make their own calculated decisions about when and where to swim. While we cannot guarantee the quality of the water on the day of each event, we know that in general in the summer months when our events take place, we have good water quality for swimming on our stretch of the Thames.
We are part of a large and active swimming community in and around Henley. Many people return again and again to our events as well as enjoying regular, problem-free swimming in the Thames. We test the water and monitor factors that may negatively impact water quality, but we cannot guarantee an absence of pathogens. We are open water swimmers and we want to continue enjoying swimming as safely as possible in such a special location for many more years to come. We advise swimmers to take some simple steps to mitigate risks further. These can be found on the FAQs section of our website.
We continue to monitor the situation carefully, but currently expect all of our swimming events to go ahead. Our normal cancellation and refunds policy applies as stated in our FAQs
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