Rowers on the River Thames are becoming ill each week due to poor quality of water ahead of the annual Oxford-Cambridge boat race on 13 April 2025.

Rowing clubs along the course are facing weekly medical absences, with members being informed that they are at an increased risk of sepsis, kidney failure and diarrhoea as a result of pollution.

At last year’s event, the 196-year-old tradition of throwing the winning cox into the Thames after the event, did not take place due to concerns over the presence of E. coli in the water. It is unclear if the tradition will be able to return this year.

Last year, the River Action campaign group found 2,869 E. coli colony-forming units (CFU) per 100ml of water before the event, which informed the decision. The safe level should be below 1,000.

Over the last month, data from Fulham Reach boat club found variation in levels of E. coli. There was a range from 350 units, which is excellent bathing waters, to over 6,500 units, which is beyond poor and unsafe.

Organisers of the boat race have suggested that testing in the week of the event will lead to a decision about the “cox toss”.

Olympic gold medallist and three-time Cambridge rower Imogen Grant said that “the health of our rivers has not improved since last year.”

“I’m not really sure that people are aware of just how bad the Thames is. As rowers, we have known the state of the water quality has not been good for years,” she added.

Petrol-powered launches, which follow boats in training and races leave traces of oil on the water. Numbers of these launches following the Boat Race have reduced over the years, but they still come out in numbers.

Rowing is a minimally polluting sport, but effects remain. Boats are washed after each session, with some clubs still using washing-up liquid which can affect the water of the river.

The Boat Race has not yet introduced electric launches, which would remove this impact.

A spokesperson for the Boat Race company said: “We are always looking at ways in which we can be more sustainable. Electric launches are one solution we are exploring to help reduce our environmental impact.”

They added: “Since 2019, an initiative between Putney’s pubs along the Boat Race course has helped to reduce plastic waste by providing reusable cups that can be washed and reused up to 50 times.

“We remain committed to finding new ways to help contribute to a greener future, on and off the water,” they said.