Samples show the water quality at Wallingford's bathing site was 'poor' during the 2025 season for the second year in a row.
Regular water testing during the swimming season began at Wallingford Beach in 2024 when the spot by Wallingford Bridge on the River Thames was made a designated bathing water site.
The Environment Agency's bathing water site profile shows water samples from Wallingford had bacteria levels which fell within the threshold for 'poor' quality, the lowest rating it could receive, for the second consecutive year since testing began.
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Claire Robertson, project officer for the Oxford Rivers Project at Thames21, explained the overall quality is marked against a "strict" rating system.
Wallingford beach on a busy summer day(Image: Jo Robb)
"The rating system is strict, in that if only one sample out of 20 exceeds the threshold levels, the bathing water gets rated 'poor'," she said.
"Wallingford seems to be generally low in bacteria levels, with the occasional spike, which is sometimes related to heavy rainfall.
"The Environment Agency and Thames Water have active investigations into what causes these spikes but it is difficult to pinpoint."
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Being a designated bathing water site does not make a site safe to swim in.
It obligates the Environment Agency to regularly test the water for bacteria levels and publish the results so that river-users can make informed decisions on entering the water.
The tests check for two types of bacteria, E. coli and intestinal Enterococci, both of which can cause serious illness, including vomiting and fever.
(From left) Cllr Holder, former deputy mayor of Wallingford, Cllr Rouane and Cllr Keats-Rohan at Wallingford Beach last year(Image: South Oxfordshire District Council)
At Wallingford, which is one of 500 designated bathing water sites in the UK but one of only 16 on rivers, South Oxfordshire District Council installed a noticeboard at the beach so people could check the latest test results before heading into the river.
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Ms Roberston said: "Swimming in the river is so good for you and is what the people of Oxfordshire have done since time immemorial.
"Nevertheless, like lots of other things in life, it carries some risk."
Tips from Thames21 on how to stay safe when river swimming include not swimming for 48 hours after heavy rainfall, covering cuts or wounds, washing your hands with clean water after swimming, and being aware of other risks in the river, including fast currents, cold water and submerged objects.
Ms Robertson added: "People have to make their own decisions whether they swim at 'poor' rated spots, remembering that outdoor swimming, like all other sports, comes with many benefits but also some risks.
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"It also depends on people's own health and bodies - for instance, I've followed our safety tips, and I haven't ever become unwell after six years of regularly swimming in the river.
"However, someone older, or with a compromised immune system might not have had the same experience."
She said that bathing water sites give Oxfordshire's rivers long term protection, and each designation results in improvements to river health.
"You can't improve something you don't monitor," she added.