Following recent heavy rainfall, “water quality in the Seine has remained below acceptable standards for safeguarding swimmers’ health,” World Aquatics said in a statement on Sunday.

“Based on this weekend, it is clear that further work is needed with Paris 2024 and local authorities to ensure robust contingency plans are in place for next year.”

Friday’s training had already been cancelled and the women’s race was postponed from Saturday to Sunday in the hope the water quality would improve.

Heavy rain in Paris for the past week has caused sewers to overflow, polluting the Seine with wastewater.

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Pierre Rabadan, a deputy to Paris Mayor Anne Hidalgo responsible for the Olympics and the Seine, said he was “disappointed” for the athletes.

Speaking to reporters in front of empty pontoons set up for the event, he said real-time readings by city hall indicated a “good” water quality on Sunday morning.

But the excessive levels of E. coli were measured in water samples taken 24 hours previously, meaning the cancellation came down to a “few hours”, he said.

World Aquatics president Husain Al Musallam said the body was “disappointed” by the cancellation. “But the health of our athletes must always be our top priority,” he added.

The federation said it “understands that further infrastructure projects will be completed to significantly improve water quality in the Seine” before next year’s Olympics.

“World Aquatics remains excited at the prospect of city-centre Olympic racing for the world’s best open water swimmers next summer,” it said.

Authorities remain ‘confident’

The Paris Olympics organising committee and local authorities have repeatedly said that recent rainfall in the French capital has been unusually high.

The committee said it would continue to “attentively monitor” water quality in the Seine in the “confident hope” that athletes will compete in the river during a triathlon later this month.

Brigitte Legare, an official in charge of competitions in central Paris, said a spare day was available if the Olympic events had to be delayed but insisted the Seine would host them as planned.

“Plan B is swimming in the Seine. I am confident… we’ll get there,” she said.

Work is ongoing on a water storage facility next to the Seine capable of holding 50,000 cubic metres of water that is due to be ready for 2024.

The planned events are also a prelude to the future return of swimming in the Seine promised by Hidalgo from 2025 on three sites where swimming has been prohibited since 1923.

Olympic open water swimming has frequently been hit by pollution concerns. At the end of the test event in 2019 ahead of the Tokyo Olympics, swimmers protested against the quality of the water in Tokyo Bay.

At the Rio Olympics in 2016, the prospect of swimming in the polluted Guanabara Bay also made headlines.

READ MORE: Will people really be able to swim in Paris’ Seine river in 2024?