Is the Seine safe for Olympic competition? So far, the answer is no

It's been a topic of conversation for months: Will the Seine be clean enough for swimmingafter French officials spent more than $1.5 billion US to clean the polluted river?

The answer on Sunday was no. And again on Monday, as Paris Olympic officials cancelledpre-race triathlon training sessionsset to take place in the Seine, citing water quality issues after heavy rainfall over the last couple of days.

A senior Olympic official promised the water quality will get better soon, with the first triathlon event set for Tuesday in the Seine.

"We are still very confident," Paris 2024 executive director of communications, Anne Descamps, said on Sunday.

World Triathlon officials also expressed confidence that the river will be safe to swim in by Tuesday, according to The Associated Press.

The Seine as an Olympic venue

The Seine was the star of the show at the opening ceremony on Friday. Delegations travelled by boat down the more than 700-kilometre long river that runs through Paris.

That went off without a hitch, but the Seine is also supposed to play host to the swimming portion of the triathlonand open-water marathon swimming, which starts on Aug. 8.

So, what's the problem? There are two main issues at play here, according to Jordan Peccia, who teaches environmental engineering at Yale University.

The first is that the Seine runs through a major city, and when it rains (and anyone who watched the opening ceremony on Friday saw just how much it rained), the water hits non-permeable surfaces like concrete and runs into sewers, which discharge into the river.

But the bigger problem, according to Peccia, is that Paris, like many other old cities, has a combined sewer system where wastewater and runoff are combined.

"It all goes to a wastewater treatment plant and it can all be treated," Peccia told CBC Sports.

That can cause sewer backups that create messes in basements, and even toilet backups.

To avoid that, they use a combined sewer overflow to redirect that mix of rainfall and sewage, dumping it directly into the river, Peccia explained.

"Paris has done a lot to try and prevent this, and this was the reason for that large tank that they could store some of that water and they wouldn't have to discharge into the river," he said.

"But it's just a possibility that with a large enough rainfall event, it can become overwhelmed."

It's not a problem unique to the Seine. There were concerns about water quality leading up to the 2016 Olympics in Rio, too, both due to sewage and the prospect of floating garbage.

A study in the British Journal of Sports Medicine looked at the rates of injury and illness among athletes who competed at the Rio Olympics, and foundabout 12 per cent of open-water marathon swimmers reported illness during the Games.Water quality didn't appear to be an issue for the Canadian delegation in Rio, though.

Did the billion-dollar fix work?

Officials did three things to try to improve water quality in the Seine, according to Peccia. The first was connecting older homes and houseboats, which were discharging waste directly into the river, to treatment plants.

"The other thing they did is they put inactivation technologies chlorine or ultraviolet light at the end of wastewater treatment plants to make sure they inactivate all the microorganisms from the wastewater that might be discharged in the clean sewage water that then enters back into the river," Peccia said.

The third was building abig holding tank to collect the rain water.

"Given how old Paris is, it's pretty remarkable they were able to build this big holding kind of chamber underground and send that water to the wastewater treatment plant," said Heather Murphy, an associate professor of pathobiology at the University of Guelph.

But she questioned whether it will be enough, given the historical pollution in the river. She said some organisms can survive in the sediment at the bottom of the river, and it may take a while to fully clean it.

Will the Seine be safe by Tuesday?

Organizers believe water quality will improve within 24 to 48 hours after rainfall.

"We've seen what were the dynamics of the Seine over the past few weeks, and that's what makes us confident," Paris Deputy Mayor Antoine Guillou said Sunday.

The exact test results that triggered officials to cancel Sunday's practice hadn't been made public as of Sunday afternoon, so it's not clear just how bad the water was.

If it's not safe by Tuesday, when the men's triathlon is scheduled, the plan would be to delay the event and hope it's safe on another day. If they run out of time the women's triathlon is scheduled for Wednesday and the mixed relay for Aug. 5 then the swimming portion of the triathlon could be cancelled, meaning competitors will only do the cycling and running.

"Hopefully we get a swim, bike, and run, because I don't swim this much to just run and bike," American triathlete Taylor Spivey said on Saturday.

Marathon swimming could move to the Vaires-sur-Marne Nautical Stadium, which is hosting rowing and canoe/kayak events, if it's not safe to host it in the Seine.

That's a higher threshold than what Murphy would consider to be safe. Beaches in Ontario are closed when more than 200 colony-forming units of E. coli per 100 millilitres of water are detected.

It's an issue the Canadian Olympic Committee is keeping an eye on.

"We recognize that in any open water swimming event there are uncontrollable variables and athlete safety must come first," said Dr. Mike Wilkinson, the COC's chief medical officer.

"We are working with the organizing committee, monitoring the detailed testing data and remain confident that the events can take place safely."

Preparing to swim in the Seine

American triathlete Seth Rider said athletes raced in the Seine last year at a test race, and he doesn't think anyone got sick.

"That can't be said about all the races we do," he said.

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German marathon swimmer Florian Wellbrock seemed more concerned about the prospect of swimming in a current, which he worries is too strong for a 10-kilometre race.

"I am really happy that the IOC and World Aquatics have a plan B for another venue," he said on Thursday.

Spivey said athletes have been increasing their probiotic intake to make sure they could withstand any potential gastrointestinal illness, while Rider suggested he's been trying to increase his E. coli threshold by doing things like not washing his hands after going to the bathroom.

Murphy isn't a medical doctor, but that's not a strategy she would endorse.

"I wouldn't say stop washing your hands, because you can then get viruses and things that are going to get you sick before the Olympics," she said.