A survey launched by British naturalist Steve Backshall has found the River Thames to be the bacterial equivalent of "untreated wastewater" causing concern among open water swimmers in Oxford.

The TV presenter, who is the president of the Berks, Bucks and Oxon Wildlife Trust, collected water samples from a Thames Water sewage treatment facility across the border in Buckinghamshire, following a sewage discharge of around 12 hours into the waterway on March 13 and 14.

He sent the samples to the wastewater research centre at Bangor University, where he is a senior honorary lecturer, and received the “horrifying” results of specialist lab tests this week.

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The findings show bacterial levels that are tens of thousands of times higher than acceptable concentrations and demonstrate a considerable risk of both people and wildlife contracting norovirus, enterovirus and E. Coli.

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This has caused unease for members of a Oxford open water swimming group, including Kit Yates, an author based in Oxford, who regularly swims in the Thames from King’s Lock to the bottom of Port Meadow.

He said: “Certainly knowing there is likely to be sewage in the water makes swimming in the river less attractive.

“Certain members of our group won’t go near the water any more either due to stories in the media highlighting the issue, hearing the experiences of friends or from having a bad experience personally.

“Personally I try to take more precautions when I swim. For example, I don’t put my head under the water if we swim in the winter.

“It’s obviously not going to be beneficial for humans to ingest untreated sewage so you can’t help but be concerned for your own health.

“More widely though I’m concerned about the impacts of the pollution of our waterways on our plants and animals."

Mr Yates believes water companies need to invest more in sewage treatment facilities and other infrastructure to alleviate the problem.

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Bicester Advertiser: Kit Yates open-water swimming with a group on the River Thames

He continued: “Currently there seems to be little incentive for them to do so.

“It feels like the whole system is broken and needs a revamp, otherwise there is little to no hope of meaningful change.”

Last month, a University of Oxford rower told the BBC his boat race crew had suffered an E. Coli outbreak because of the high levels of the bacteria in the water.

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Thames Water uses storm overflows to discharge excess waste and rainwater from its combined sewer system to nearby rivers and seas during periods of heavy rainfall.

The overflow helps to stop rainwater and sewage from overwhelming the pipe network and backing up into people’s homes and streets.

However, it has come under fire following an increase in the use of storm overflows over recent months, sometimes even during dry weather.

Data from the Environment Agency (EA) shows a 54 per cent rise in spills from 2022 to 2023, something the organisation said was partly due to England experiencing its sixth-wettest year on record.

Helen Wakeham, director of water at the EA described the findings as “disappointing” but “sadly not surprising”.

Recent government action on the issue includes a consultation to ban water bosses’ bonuses when criminal breaches have occurred, quadrupled company inspections, a fast-tracked £18 million investment to cut spills and a whistleblowing portal encouraging workers to report breaches.

A spokeswoman for Thames Water said the company planned to host Mr Backshall alongside the River Action Group on a visit to the Little Marlow Sewage Treatment Works in Buckinghamshire.

She added: "Little Marlow Sewage Treatment Works is fully compliant with its effluent quality consent and its storm discharge permit, as set by the Environment Agency to protect river water quality and the associated ecosystem.

"There are clear guidelines on how samples should be taken in order to give an accurate picture of the quality of the water and we would be keen to understand more about the approach taken in this instance.

"Taking action to improve the health of rivers is a key focus for us and we are leading the way with our transparent approach to data.”

Additional reporting by Eleanor Burleigh.