For Britain’s team of gold medal-chasing triathletes, no stone has been left unturned at these Paris Olympics. They scrub their wetsuits with Hibiscrub disinfectant every time they enter a river. They use probiotics, mouthwash and Coke to further protect against E coli. And recently they have even developed a special trisuit that is more buoyant and aerodynamic to gain a further edge.

However, there is one thing for which Team GB has found it impossible to prepare: rising sewage levels in the Seine. The heavy rain on Friday and Saturday has already led to both swimming practice days in the river to be cancelled. And now it has put the men’s race on Tuesday on a knife-edge.

So when Team GB’s Alex Yee sets his alarm on Monday evening, he will not be entirely sure what will happen next. He might be racing a few hours later at 8am local time. He might have to wait until a reserve day later in the week. Or, in extreme circumstances, his Olympics might involve just riding a bike and running.

While Yee – who is favourite for gold – is sleeping, organisers will get to work. At around 3.30am they will measure a series of points in the Seine, where the triathletes are due to swim 1500m, before going on a 40km bike ride and a 10km run, and announce their decision shortly afterwards.

It promises to be a close-run thing as Étienne Thobois, the chief executive of Paris 2024, acknowledged. “We have to wait,” he said. “We don’t do fiction scenarios.

“We are very respectful of the athletes. They are the heart of the Games. We have done everything we could in relation with the international federations and public authorities to achieve the goal of swimming in the Seine which will be a fantastic legacy.”

That certainly is true. Swimming in the Seine has been banned for over a century. But since 2015, organisers have spent around £1bn to ensure a cleaner river for the Games – and to allow Parisians to swim in it afterwards.

Renovations have included the construction of a giant basin to capture excess rainwater and stop too much sewage from flowing into the river – as well as renovating infrastructure and upgrading wastewater treatment plants. The hope now is that the forecast hot weather will be enough to drop E coli levels low enough to race.

“We are still optimistic, we have a contingency plan, we hope when they wake up they will be able to participate,” Thobois said. “As you could see there has been quite a lot of rain in the last couple of days. We are monitoring very closely. The level is going down rapidly, the forecast is bright and shiny. We are confident we will be able to hold the competition and we still have a contingency plan for Friday just in case.”

Assuming all goes well, Team GB’s triathletes could have extremely successful Games. Last year Yee won the men’s test event in Paris, while Beth Potter won the women’s equivalent. For good measure, Britain are also favourites for next week’s mixed relay.

On a course where it is expected to be hard to breakaway on the swim or the bike, it also helps that Yee and Potter are exceptional runners. The 26-year-old Yee competed for GB’s in the 10,000m at the European Athletics Championships in 2018, while the 32-year-old Potter ran over the same distance at the 2016 Olympics.

No wonder Mike Cavendish, GB triathlon’s performance director, is confident of a strong showing from Yee, Potter and the rest of the British team.

“Alex’s cycling is massively underappreciated,” he said. “He is pushing not far off Tour de France numbers over a shorter distance and he is a much better cyclist than people give him credit for. We’ve also done a huge amount of work with him from an open water perspective. So if he has a good swim, I wouldn’t be betting against him.

“The same applies to Beth. She has worked with the 2012 and 2016 gold medallist Alistair Brownlee and there aren’t many people who know much more about the sport than him.”

Cavendish concedes that other teams are also strong, especially the French. But, to British eyes, the triathlon course around the Pont Alexandre III bridge looks to be the place to be in the coming days – assuming, of course, the Seine keeps itself clean.