Competitors in a triathlon have told the BBC they have suffered from vomiting and diarrhoea after swimming in the River Thames.

Rebecca Norman, from Reading, said she had to go to A&E after feeling sick 24 hours after the Royal Windsor Triathlon on Sunday.

The 21-year-old shared her experience on social media and had seen several other people also report being seriously ill since the race.

Organisers Human Race said it conducted water tests in the weeks leading up to the event and on the day which “met the standards set by the British Triathlon Federation (BTF)”.

It added the “handful of reports of illness we have received are consistent with previous” runnings of the event.

Thames Water said people would be “misinformed to automatically conclude” the issues were caused by its activities and said its nearest sewage treatment works in Slough had not discharged since early April.

Miss Norman told BBC News: “I was throwing up blood, feeling faint, had a fever, exhaustion and the worst stomach cramps I have ever experienced.”

“I specifically emailed the race organisers before the event about my concerns of the water and they promised to sample the water a week before,” she said.

Miss Norman shared the message from Human Race with the BBC which said: “Absolutely no risks are taken regarding the conditions and your safety.

“We usually send several samples of water from the Royal Windsor Triathlon swim section for tests in a lab the week leading up to the event.”

Human Race said it would cancel the swim if there were concerns.

Dan Rosam, 35, a civil engineer from Surbiton, said 40 hours after he took part in the event – his first triathlon – he started to feel unwell.

He noticed on social media other competitors were also feeling sick and he claimed it was “too much of a coincidence”.

Mr Rosam admitted he was “apprehensive about swimming in the water beforehand”.

“I had faith in the organisers who said they had tested the water and would cancel it if it was unsafe,” he said.

“I feel a bit let down by them and it’s put me off doing it again.”

Last month, The Boulter’s to Bray Swim in Maidenhead was cancelled because of fears about sewage in the River Thames.

Mr Rosam, who has been off work ill, blamed pollution in the water, adding: “It’s disgusting that the water companies are taking money and passing it on to their shareholders but they’re not putting any of it into fixing the infrastructure.”

Connie Wright, 32, from south-west London, said she woke up on Tuesday morning with a “severe stomach bug”.

“Given the number of people affected, it seems likely the water may have been compromised,” she said.

A spokesperson from Human Race said: “As part of our procedures, we conduct water quality tests in the weeks leading up to the Royal Windsor Triathlon. Additionally, we send a further test to the lab on the morning of the event.

“Due to the additional stories in the media this year, we performed two additional tests in advance of the event, making three in total, all of which met the standards set by the BTF.

“As with all open water swimming events, a small number of participants may pick up stomach bugs.

“We send regular emails to all participants in advance of the event that cover event information and safety.

“This year was our biggest Royal Windsor Triathlon since 2018, with over 2,000 people taking part.

“Currently, the handful of reports of illness we have received are consistent with previous editions. Our team will continue to monitor the situation.

“We are collaborating with BTF to explore how we can support efforts to address the wider issue of water quality across the UK to help ensure future generations can continue to participate in fantastic sports such as triathlon.”

A Thames Water spokesperson said: “River health is not the sole responsibility of Thames Water and there are many factors which influence river quality including pollutants, animal faeces from livestock and wildlife, along with run-off from farms and roads.

“It would therefore be misinformed to automatically conclude that this is a result of Thames Water activities.

“Our nearest sewage treatment works in the area is Slough, and it has not discharged since early April.”