Belgium has pulled out of the mixed triathlon in Paris after one of its competitors fell ill while swimming in the River Seine.

Uncertainty surrounds the final Olympic triathlon event in Paris because of renewed concerns regarding water quality in city’s waterway.

The mixed relay was due to be held early on Monday (local time) but could be pushed back after heavy rain on Wednesday and Thursday again caused levels of bacteria in the water to rise.

For at least one team, even a delay won’t convince them to plunge back into the Seine.

The Belgian Olympic and Interfederal Committee said on Sunday that Claire Michel, who finished 38th in the women’s triathlon on Wednesday, was “unfortunately ill and will have to withdraw from the competition”.

While the statement did not elaborate on Michel’s illness, Belgian media has reported it is E. coli. Newspaper De Standaard reported that Michel was taken to hospital for treatment.

“She was infected with E. Coli bacteria, an examination revealed. That bacterium can cause gastrointestinal problems. The cause may be the polluted Seine,” the paper wrote.

It follows numerous concerns about the river’s water quality.

Elsewhere, Switzerland announced one of its competitors, Adrien Briffod, had also had to withdraw from the race because of a gastrointestinal infection. He will be replaced by Simon Westermann.

Swiss Olympic chief medical officer Hanspeter Betschart said it was unclear if Briffod’s infection was related to the quality of water in the Seine.

“A survey of my colleagues from other countries has so far not revealed any accumulation of gastrointestinal illnesses among the athletes who started the individual race last Wednesday,” Betschart said.

Games organisers have said that bacteria levels in the Seine are at a level that is considered safe for the athletes.

But in a pointed comment, the Belgian committee said it “hopes that lessons will be learned for future triathlon competitions at the Olympic Games”.

“We are thinking here of the guarantee of training days, competition days and the competition format, which must be clarified in advance and ensure that there is no uncertainty for the athletes, entourage and supporters,” the statement said.

Last week, the men’s race was changed from Tuesday to Wednesday, the same day as the women’s competition, and athletes were unable to swim in the river until the day of the race.

Throughout the competition, athletes have largely trusted Games organisers’ assurances about the quality of the water in the river.

“The swimming was fine during the race. We know that they took samples this morning. They take a lot of time to analyse, so we don’t know the results obviously,” women’s silver medallist Julie Derron of Switzerland said.

“We all trust the authorities and the organisers that they keep us safe. And so we had a safe race today.”

The men’s gold medallist, Alex Yee of Great Britain, was also complimentary.

“We’re lucky enough to have probably the most beautiful venue of any race in the Olympics. And I guess that came with a small penalty of the risk of the Seine being dirty,” he said.

Race organisers issued a statement on Sunday, following a meeting on Saturday night.

“[The] decision has been made to cancel the swim leg of the triathlon familiarisation, which was due to be held on August 4 at 8am,” it said.

“Given the heavy rain over the nights of July 31 and August 1, which had been particularly intense upstream of Paris, we still see impact on the water quality in our venue.

“We are expecting an improvement on the conditions in the next hours, but not to a level to which the swim familiarisation planned for [Sunday] can take place.”

At Sunday morning’s IOC briefing, Paris 2024 director of communications Anne Descamps said: “We are expecting improvement regarding the weather forecast. As we’ve seen the sun and the heat have a very positive impact.”

-with AAP