Test results released on Friday showed dangerously high levels of E. coli bacteria in water from the Seine, less than two months before the swimming events at the Paris Olympics.
Pollution levels during the first eight days of heavy rain in Paris in June showed bacteria such as E. coli and enterococcus exceeded the threshold deemed safe for athletes.
The report was released by watchdog group Hauts de Paris a day after a senior International Olympic Committee official said there was “no reason to doubt” the race would go ahead as scheduled in the historic city centre along the Seine river near the Eiffel Tower.
The first Olympic event on the cleaned Seine will be the men's triathlon, which includes a 1.5-kilometer (less than a mile) swim, on the morning of July 30. The women's triathlon will be held the following day, and the mixed relay will be held on Aug. 5.
French President Emmanuel Macron said on Monday that the opening ceremony of the Paris Olympics, planned for the Seine River, could be moved to the Stade de France if the security threat is deemed too great.
The women's and men's 10-kilometer (6.2-mile) marathon swims are scheduled for Aug. 8 and 9, respectively, in waters that were historically polluted before a $1.5 billion investment was made ahead of the Olympics.
“We are confident that people will be able to swim in the Seine this summer,” IOC chief Christophe Dubi said in an online briefing on Thursday after hearing updates from Paris city authorities and the Olympic organizing committee.
Despite the IOC's public expressions of confidence, the final decision on whether to approve an event as safe for athletes must rest with the respective sports' governing bodies, World Aquatics and World Triathlon.
The safety of the Seine's water at the Olympics has been called into question after some planned test events last August were cancelled due to unseasonable heavy rains.
According to European standards, the safe limit for E. coli is 900 colony-forming units per 100 milliliters, the same standard used by the World Triathlon Federation to determine whether water is good enough for competition.
For the first eight days of June, test results showed E. coli levels frequently exceeding these thresholds. Enterococcus levels were more favorable, remaining mostly within the safe range. Tests showed improvement from high contamination levels on June 1 to acceptable levels by June 9, primarily due to improving weather.
Rainwater seeps into the sewers, and excess water laden with fecal bacteria is dumped into the Seine to prevent roads from flooding. To deal with this, a huge reservoir was opened in May that can store 50,000 cubic metres of water during heavy rains.
Water quality in major urban rivers can be affected by a variety of factors, from runoff to chemical dumping (sometimes illegally) to boat traffic.
Earlier this week, Paris Mayor Anne Hidalgo reiterated her promise to swim in the river before the start of the games. On Tuesday, she confirmed she would postpone the swim until after France's general election, which ends on July 7.
