Angry river users will splash out against Thames Water sewage spills in a protest on Monday evening near the company's headquarters.
In an action coordinated by River Action and Surfers Against Sewage campaigners who have been alarmed at water pollution with stage a paddle-out around 5.30pm.
The campaigners said this action follows localised water quality testing by citizen scientists in the area which have revealed that E.coli is present in the water.
The testing between June 9 and 19 found an average of 741 E.coli colony forming units (CFUs) per 100ml - which is considered just below the Environmental Agency's poor water quality level of 900CFUs for bathing water quality standards.
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Activists said this indicated sewage was present in the river near to the headquarters of Thames Water in Reading and could cause sickness.
Chloe Peck from River Action, the group that supervised the water quality testing, said: “It is ironic that the testing we’ve done on the water near to Thames Water’s HQ indicates the river there is just about safe to swim in because wherever else they operate and we have taken water samples their sewage pollution presents a major health risk.
“Earlier this year we found extraordinarily high levels of E.coli on the Thames used for the university boat race - 9,500CFUs - and in that case rowers did get very sick.
"Nothing short of a total overhaul of the water regulators and refinancing of Thames Water - putting people and nature before profit - will do.”
Surfers Against Sewage chief executive Giles Bristow also slammed Thames Water.
He said: "Thames Water’s greedy, grasping hands are stained with the utter filth they have been spewing into this iconic river.
"Our waterways should be havens for wildlife and wild swimmers but these precious public spaces have been hijacked by an industry single-minded in its pursuit of profit."
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A Thames Water spokeswoman acknowledged that all discharges were "unacceptable" but said that the sewage system was "historically designed to work in this way, to prevent sewage backing up into people’s homes".
She said: “We know how much rivers are loved and enjoyed by everyone, and we are committed to seeing our waterways thrive, but we can’t do it alone.
"Farming, industry, livestock and more extreme weather also play a role in river health.
"We have published plans to upgrade 250 of our sites across the region.
"At the vast majority of our sites this will increase capacity and reduce the number of necessary discharges."
The spokeswoman also said more investment was needed across the entire sector, as infrastructure aged and demand on it increased.
She added: "That’s why we’ve asked for increased investment in the next regulatory cycle between 2025-2030."
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