Oxford University Boat Club have confirmed three members of their men’s team were suffering from a stomach bug before their Boat Race defeat by Cambridge on Saturday, but said they could not identify the specific cause.

Following a double success for the light blue of Cambridge in the women’s and men’s events Lenny Jenkins, the Oxford men’s seven seat, said: “We’ve had a few guys go down pretty badly with E coli strain … It would have been ideal not to have so much poo in the water.”

A club statement released on Sunday afternoon said they could not confirm E coli – shown to be present in dangerously high levels on the River Thames course before the event – was to blame.

“Three members of the OUBC men’s blue boat came down with a stomach bug in the week of the Boat Race, the origin of which we cannot definitively say,” the statement said.

“These things happen in the final lead up to the race, including in years we have won. We want to again congratulate Cambridge’s men on an exceptional race performance and a well-deserved victory.”

Asked if they planned to test for E coli the OUBC said: “The athletes received medical advice and treatment which does not include testing in the first instance.” Organisers of the Boat Race had earlier on Sunday contacted Oxford to seek further clarity on the cause of the sickness bug.

James Wallace, the chief executive of River Action, whose pre-race testing highlighted dangerous pollution in the water, told the Guardian: “Let’s be clear. Rowers being sick from training and racing on the Thames is not new, and nor is the news of Thames Water discharging billions of litres of untreated sewage into the river.

“E coli at these high levels can only come from sewage, both raw and treated … Thames Water is the only company responsible for sewage treatment on the Thames.”

Thames Water has blamed high rainfall but the Government is under increasing pressure to act. The company’s renationalisation is not being ruled out following shareholders’ refusal to release further investment.

“It’s obviously not a great situation,” the Cambridge men’s coach, Rob Baker, said following the victory on Saturday. “We’d like cleaner waterways, I think that’s fair to say. We’d like to not have such a risk for our athletes.”