Campaigners have contested the public claims by Thames Water that River Action was "alarmist" when it claimed the stretch of the Thames used for the Henley Royal Regatta was unsafe.
The call comes in an open letter to the CEO of Thames Water Chris Weston signed by British Rowing, a member of the House of Lords, the mayor of Henley and environmentalist famous faces Feargal Sharkey and Steve Backshall.
River Action has shared the open letter, which includes asking Thames Water to "properly invest in infrastructure improvements" and "correct the record on water quality", with the Secretary of State for the Environment, Steve Reed MP.
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Last month River Action claimed there were "alarmingly high" levels of E.coli on the Thames used for the Henley Regatta, the world's biggest international rowing event in the calendar, and a part of the river used for swimming events involving thousands of competitors risking their health.
The group said this followed a month of testing by the Henley and Marlow River Action Group in the lead up to the world-famous rowing competition.
According to River Action, the testing involved a World Health Organization verified E.coli device, as used by the Olympic team in France to assess water quality on the River Seine.
In response to this, Thames Water said: “We need honest and balanced debate that recognise the range of factors impacting river health, rather than an alarmist approach that tries to apportion blame in a misguided way.”
River Action said it believes that rather than being alarmist, Thames Water is "polluting all the time because they don’t remove harmful bacteria from treated water before it enters the river".
CEO of River Action James Wallace said, “Our testing was rigorous, robust, used WHO verified technology, was independently approved, and published on several websites.
"For Thames Water to call us alarmist is a joke.
"We should all be alarmed and concerned that their creaking wastewater treatment plant at Henley is causing a risk to the health of the river and river users.
"They should focus on getting their business in order rather than trying to discredit citizen scientists for calling out dangerously high levels of E.coli on the Thames.”
In response to this, a Thames Water spokesperson said: "We have received a letter from River Action UK which we will respond to in due course.
"We have been conducting testing in the River Thames in Henley since mid-May for a two month period, and have published all the results on our website, so the public can see the data and use it to make an informed choice about how they use the river.
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“We know how much people enjoy and appreciate our rivers, and we are committed to seeing our waterways thrive, but we can’t do it alone.
"Farming, industry, road runoff, wildlife and increasingly extreme weather also play a role in river health.
"We have clear and deliverable plans to upgrade 250 of our sites across the region, to increase treatment capacity and reduce the number of storm discharges including at our Henley sewage treatment works.
“As infrastructure ages and demand on it increases more investment is needed across the entire sector.
"That’s why we’ve asked for increased investment in the next regulatory cycle between 2025-2030."
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