Paris Olympics organizers canceled Tuesday’s open water swimming training in the River Seine due to pollution, raising questions about why triathletes were allowed to swim in the waterway the day before.

This marks the fifth time since the Games began on July 28 that river training has been canceled, likely adding to swimmers' frustration.

Despite a 1.4 billion euro ($1.5 billion) upgrade over the past decade, the Paris sewer system still discharges untreated wastewater into the river during heavy rainstorms.

Training for the triathlon mixed relay race was canceled on Saturday and Sunday after storms last week.

Organizers and the governing body World Triathlon had given the green light for the competition to proceed on Monday, saying bacterial levels had fallen to safe levels. They did not provide figures for the two bacteria they measure as indicators of fecal matter – E. coli and enterococci.

The race turned out to be a thriller, with Germany's Laura Lindemann holding off fierce challenges from the United States and Britain to take gold.

Organizers issued a statement early Tuesday saying the marathon swimming "familiarization session" would not go ahead due to elevated enterococci readings.

"After the daily situation meeting this morning between Ville de Paris, Paris 2024, and World Aquatics, it has been decided that the familiarization session scheduled for today, August 6, 2024, is canceled," the statement said.

Several triathletes have expressed frustration over the repeated training cancellations since the start of the Games, which have prevented them from preparing for the strong currents in the Seine, which is flowing at two to three times its usual summer rate.

The Seine is set to be used for marathon swimming – a 10-kilometer race – on August 8 for women and August 9 for men.

Monday’s mixed triathlon relay was disrupted by illness, with at least three teams reporting sick athletes who had swum in the River Seine the week before during the individual men’s and women’s races. Teams from Belgium, Switzerland, and Norway reported racers with stomach bugs, although no direct link was drawn to the Seine.

Some athletes defended using the river, saying they had not been affected by the uncertainty about its cleanliness.

"No one was afraid to jump in. We were all happy to have a race," German Tim Hellwig, who won gold on Monday during the team event, told reporters.

"If like 99% of the athletes don't have any problems, I think it's fine," he said.

Organizers have said that marathon swimming could be moved to another location in Vaires-sur-Marne on the River Marne, east of Paris, if the Seine is too polluted to use. They said Tuesday they were "very confident" that the men's and women's events would take place in the Seine.

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