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Only one popular spot for swimming and watersports in and around Oxford has bacteria at safe levels, according to a survey by a campaign group.

The seven other places in the rivers that are regularly used by swimmers, punters, rowers and kayakers were found to have levels of harmful bacteria one and a half to three times higher than recommended safe levels, a study by the Oxford Rivers Project funded by Thames Water found.

The study concluded that in most of these places the pollution came from sewage, although some places were also affected by livestock.

Claire Robertson, Oxford Rivers Project Officer at Thames21, said: “These findings confirm what we expected: that bacteria levels at our riverside recreation sites are higher than they should be. However, we don’t want people to be discouraged from swimming, punting, rowing and kayaking on Oxford’s rivers. They have a myriad of benefits, for personal health and well-being, and for the city as a whole.

“We are pleased that Thames Water has funded and supported this research. Now is the time for them and the various authorities to put in place an action plan and find the funding to reduce wastewater and agricultural pollution to safe levels, and soon.

A section of the Thames in the city, Wolvercote Mill Stream at Port Meadow, became only the second stretch of river in England to be given bathing water status last month.

The status means the waters will be measured for two types of potentially harmful bacteria between May 15 and September 30 each year.

But the Oxford Rivers Project has endeavored to highlight the quality of all the rivers in and around the city. Their study replicated tests that take place in designated bathing water areas such as Wolvercote Mill Stream.

Volunteer citizen scientists took water samples at least once a month from 18 sites in Oxfordshire and analyzed them to determine levels of E.coli and intestinal enterococci, bacteria harmful to human health.

Bacteria levels were measured in a laboratory at Thames Water, and the project was jointly funded by Oxford City Council, the Rivers Trust and Thames Water.

The study found that a site on a small stream downstream from the Church Hanborough sewage treatment plant was consistently 50 times safer for swimming, even when the sewage treatment plant was not overflowing and apparently not treating the waste.

Ten sites on smaller upstream tributaries were also sampled. None reached the level considered safe for swimming, ranging from close to safe in the Upper Thames and Windrush catchments, to seven times safe in the Limb Brook catchments and Evenlode.

Richard Aylard, director of sustainability at Thames Water, said: “Taking action to improve the health of rivers is a key objective for us. We are delighted that Wolvercote Mill Stream is now designated for swimming.

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“Our own commitments to improve the health of rivers include reducing the annual duration of sewage discharges into rivers by 50% in the Thames Valley by 2030.” Aylard said the company had planned substantial investment in its water treatment sites to reduce raw sewage discharges, including a major expansion of treatment plants at Witney in Oxfordshire.

He said the company is on track to provide live release alerts from all 468 licensed locations in the region, within an hour of when releases start and stop, by the end of 2022.

“We are clear that it is completely unacceptable for untreated sewage to enter rivers, whether permitted or not,” he said. “Stopping releases completely will take time and sustained investment, but every step we take on this journey is a step in the right direction.”

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