Tests conducted in the River Thames just before the Henley Royal Regatta revealed river pollution that could be harmful to human health, according to campaigners.
Environmental charity River Action discovered high concentrations of phosphates, nitrates, and dangerous bacteria in June.
Sir Steve Redgrave, the chairman of the regatta, expressed his "deep concern" about the river's sewage pollution.
By 2025, Thames Water plans to upgrade Henley Sewage Treatment Works, lowering discharges during inclement weather.
Level E, according to River Action. On June 20, when it rained, coli bacteria increased, posing a "significant health risk" to people who use water.
High concentrations of intestinal enterococci bacteria were also found, which is another indicator of human or animal feces.
A week later, the renowned regatta's competitors, hundreds of rowers, started to compete.
The charity added that the majority of the samples collected during the four weeks of testing contained "ecologically harmful" concentrations of phosphates and nitrates.
"The testing demonstrates that the Henley mile is severely degraded by sewage pollution," it said in its conclusion. ".
James Wallace, the charity's chief executive, said: "The outcomes of this citizen science demonstrate the dire condition of England's capital river. The wildlife along the Thames is dying off, putting river users in grave danger. ".
The charity claimed that the river's status would have changed from "good" to "poor" if bathing water standards had been applied.
"At the Henley Royal Regatta, we are extremely concerned about the effects that sewage pollution is having on our lovely river," said Sir Steve.
"I canoe from my home town of Marlow at Longridge. Sometimes you can tell that there has been a discharge by the color of the water; it's not a place I'd ever want to fall into. ".
Thames Water stated: "We consider all sewage discharges without treatment to be unacceptable.
"We recently announced our plans to invest £1 point 6 billion in our sewage treatment works and networks over the next two years, and we are working hard every day to reduce the discharge of untreated sewage into our rivers.
. "
