PARIS (AP) — The Olympic men’s triathlon scheduled for Tuesday has been postponed due to concerns about water quality in the Seine River in Paris, where the swimming portion of the race would take place.

Organizers said they plan to hold the men’s triathlon on Wednesday instead. The women’s competition is also scheduled for Wednesday, but both are subject to water testing. Friday is also set as a backup date.

But Meteo-France, the French weather service, predicted storms on Tuesday evening, light rain on Wednesday afternoon and storms on Thursday, which could complicate the rescheduling of the events.

Heavy rainfall usually causes concentrations of E. coli and other bacteria to rise in the Seine. Paris has had a downpour during the Olympic Opening Ceremony Fridaywith rain continuing into Saturday. The swimming portion of the training events, designed to familiarize the triathletes with the course, was cancelled on both Sunday and Monday due to concerns about water quality.

The decision to postpone the men’s triathlon followed a meeting early Tuesday morning involving the sport’s governing body, World Triathlon, the medical team and city officials.

“Despite the improvement in water quality in recent hours, values ​​​​are still above acceptable limits at some points of the swimming course,” the organizers said in a statement announcing the postponement, stressing that their “priority is the health of the athletes.”

The men’s event is now scheduled to begin at 10:45 a.m., which could make the heat more of a factor. Wednesday’s high is forecast to be 95 F (35 C), and the event could end at the hottest time of the day. The women’s race is scheduled to begin at 8 a.m. Wednesday, as originally planned.

Organizers and city officials had expressed their confidence that bacteria levels would improve as the air cleared and temperatures rose in the days that followed. But that was apparently not enough to ensure the safety of the athletes.

Paris has made a huge effort to improve the water quality of the long-polluted Seine, so that the swimming portion of the triathlon and the marathon swimming event in August could be held in the famous river that flows through the city center. But bacteria levels are still fluctuating.

Daily water quality tests measure the amount of fecal bacteria known as E. coli, with a safe limit of 900 colony forming units per 100 milliliters determined by European regulations. Monitoring group Eau de Paris publishes data every Friday, but it is only updated through the preceding Tuesday.

High levels of E. coli in water can indicate sewage contamination. Most strains are harmless, and some live in the intestines of healthy people and animals. But others can be dangerous. Even a mouthful of contaminated water can cause diarrhea, and the germs can cause illnesses such as urinary tract or intestinal infections.

Efforts to make the river suitable for swimming cost 1.4 billion euros ($1.5 billion). These included the construction of a gigantic basin to collect excess rainwater and prevent wastewater from entering the river, by renovating the sewerage infrastructure and modernising the wastewater treatment plants.

Mayor of Paris Anne Hidalgo took a dive very publicly in the river two weeks ago, along with the president of Paris 2024, Tony Estanguet, and the top government official for the Paris region, Marc Guillaume, along with swimmers from local swimming clubs. Data released last week shows that the E. coli levels in the Bras Marie that day were 985 units per 100 milliliters, slightly above the established threshold value.

Other swimming events scheduled for the Seine include the mixed triathlon relay on August 5 and the women’s and men’s marathon swimming events on August 8 and 9. ___

AP Health Journalist Devna Bose contributed from Jackson, Mississippi.

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