The men’s individual triathlon in Paris 2024 was postponed on Tuesday after tests showed the water quality of the Seine River did not meet acceptable standards.

With organizers now saying there is only a 60% chance that both the rescheduled men’s and women’s events can take place on Wednesday, it only adds to the uncertainty surrounding the event.

BBC Sport discusses all the key questions surrounding the triathlon and possible contingency plans.

On Tuesday, organizers reported that E. coli bacteria found at four points along the 1,500-meter course, less than 24 hours before the postponement, were the biggest concern.

According to European standards, the safe limit for E. coli is 900 colony forming units (cfu) per 100 ml. The four measurements ranged from 980 to 1,553 cfu per 100 ml.

Data from July 17 to 23 showed that the river that crosses the French capital was suitable for swimming on six out of seven days.

Unexpected bad weather proved to be a problem for the organizers. On the day of the opening ceremony, heavy rain fell, which increased pollution levels.

According to UK government guidelines, swimming in open water can increase the risk of stomach upsets and external infections due to microorganisms such as E. coli, and can cause serious illness.

Britain’s Alex Yee is one of the favourites for gold in the men’s event, while her teammate Beth Potter is the reigning women’s world champion.

The postponement of the men’s race was announced at 03:00 (BST) on Tuesday, four hours before the start of the race.

The women’s race will start at 07:00 BST (08:00 local time) on Wednesday, while the rescheduled men’s race will kick off at 09:45 BST (10:45 local time).

To further complicate matters, Meteo-France, the French national weather and climate service, has also forecast storms for Tuesday evening, light rain on Wednesday afternoon and more storms on Thursday.

According to the organizers, the amount of E. coli and other bacteria in the Seine has increased due to previous heavy rainfall.

While there is hope that the warm weather will reduce the bacteria count enough to allow the competition to go ahead, it could still pose a problem as the men’s competition will conclude at the hottest time of day, when temperatures are expected to reach 32 degrees Celsius.

If the triathlons on Wednesday do not take place, Friday will remain a reserve date for both events.

If the water quality is still not good enough on Friday, the organizers can, as a last resort, organize the event in the form of a duathlon, so only the cycling and running parts.

The triathlon made its Olympic debut in Sydney in 2000. The event consists of a 1,500-meter swim, a 40-kilometer bike ride and a 10-kilometer run.

Although a mixed relay was added three years ago in Tokyo, there has never been a duathlon at the Olympics. Normally, it would consist of a 40km bike ride and a 10km run.

However, during the 2023 test event in Paris, a duathlon format was tried out, with the swim replaced by an additional 5km run.

Although Olympic coaches and athletes are typically prepared for most eventualities, it is unlikely that many training plans are specifically tailored to a duathlon.

Belgian triathlete Marten Van Riel expressed his displeasure about the situation in a response to World Triathlon’s Instagram post announcing the postponement on Tuesday.

He wrote: “If the health of the athletes had been the priority, this event would have been moved to another location long ago.

“We are just puppets in a puppet show. Duathlon is not triathlon and changing the day in the middle of the night is disrespectful to the years of preparation of the athletes and to all your fans who would be watching live or on TV. What an appearance for triathlon on the biggest stage.”

American athlete Seth Rider prepares for exposure to bacteria.

“We know there is going to be some exposure to E. coli, so I try to increase my E. coli threshold by exposing myself to a little bit of E. coli in my daily life,” he said Saturday.

“Just little things throughout the day, like not washing your hands after you go to the toilet and things like that.”

The decision to start the triathlon at the Seine was seen as a historic, but also remarkable decision.

Critics argue that it was mainly for aesthetic reasons, as swimming in the river has been banned for more than 100 years due to high levels of pollution and the risk of disease.

However, French authorities have invested 1.4 billion euros (£1.2 billion) to make the Seine suitable for swimming, as a key remnant of the Games.

The works include the construction of a giant underground basin the size of a dozen Olympic swimming pools to collect excess rainwater and prevent wastewater from flowing into the river, the renovation of the sewer system and the modernisation of wastewater treatment plants.

Nevertheless, E. coli levels were still 10 times higher in June than the acceptable levels imposed by sports associations.

British triathlete Vicky Holland, who won bronze at the 2016 Rio Games, told BBC Sport: “This is a really important thing, not just for our sport but for the rest of the world.

“There are fewer and fewer waters in the world that are safe for swimmers and that’s a real shame. It really highlights that we really need to try to clean up these waters. I know they tried to do that here with Paris.

“They have invested a huge amount of money in cleaning up the Seine and they have done a very good job. It is just not quite as desired yet.”