The men’s triathlon at the Paris Olympics has been postponed because of concerns over water quality in the River Seine, despite multiple reassurances.

Swimming training for the triathletes was cancelled on Sunday and Monday and the decision has been taken to move the men’s race, which had been due to start at 8am local time (4pm AEST) on Tuesday.

It has been rescheduled to take place at 10.45am local time on Wednesday, after the women’s race which is scheduled to take place at 8am.

A statement from World Triathlon said Friday remains a contingency day if one or both of the races are unable to go ahead in the famed river that runs through the city centre.

“Tests carried out in the Seine today revealed water quality did not provide sufficient guarantees to allow the event to be held,” read the statement.

“Despite the improvement in the water quality levels, the readings at some points of the swim course are still above the acceptable limits.”

More than one billion euros ($1.7 billion) was spent on cleaning up the river in preparation for the Games, but organisers knew heavy rain in the days before a competition could cause the levels of the harmful bacteria E. Coli to rise.

High levels of E. coli in water can indicate contamination from sewage. Most strains are harmless and some live in the intestines of healthy people and animals. But others can be dangerous. Even a mouthful of contaminated water can lead to diarrhoea, and the germ can cause illnesses such as infections in the urinary tract or in the intestines.

There was hope the effects of the deluge that marred Friday’s opening ceremony would have passed in time but that has not been the case.

Paris Mayor Anne Hidalgo very publicly took a swim in the river two weeks ago, along with Paris 2024 chief Tony Estanguet, and the top government official for the Paris region, Marc Guillaume, along with swimmers from local swimming clubs.

An unnamed employee from the city’s environmental department was quoted by The US Sun last week as saying the decision to use the Seine was “insane”.

“It’s insane that the IOC and the organisation of the Olympics had that idea,” the employee said. “The water is very bad, it’s full of dirt and not proper for any activity.

“Also, the levels of chemicals, human faeces, and other dirty things are very high, so bacteria like E. coli are everywhere.”

Other swimming events planned in the Seine are the triathlon mixed relay on August 5 and the women’s and men’s marathon swimming events on August 8 and 9.

Seth Rider of the United States, one of 55 triathletes entered in the men’s race, says he took unconventional measures to prepare for exposure to bacteria.

“We know that there’s going to be some E coli exposure, so I just try to increase my E coli threshold by exposing myself to a bit of E coli in your day-to-day life,” Rider said at a meda conference on Saturday.

-with AAP