The swimming stage of a triathlon in Paris' Seine River was canceled on Sunday due to pollution, organizers announced, raising further questions about holding competitions there during the 2024 Olympics.

The mixed relay triathlon is the third pre-Olympics test event to be affected by excessive E. coli bacteria in the water, but organizers insist the Seine will be fit to host events next year.

The triathlon was changed to a duathlon only involving cycling and running after analyses of the water quality did not offer the "necessary guarantees", confirmed the Paris Olympics organizing committee and governing body World Triathlon.

The same decision was reached for a para-triathlon test event on Saturday, while the World Aquatics Open Water Swimming World Cup was canceled altogether earlier this month.

As organizers investigated the source of Saturday's elevated E. coli readings, Tony Estanguet, the head of the Paris 2024 organizing committee, noted that there was no "Plan B" for next year's Olympics.

"There is no solution to move the event, the triathlon and open water swimming will be held in the Seine next year," Estanguet stressed.

On August 6, the International Swimming Federation canceled the pre-Olympics swimming test competition after completing tests on the Seine River's water.

"Water quality in the Seine has remained below acceptable standards for safeguarding swimmers' health," a statement issued by World Aquatics read.

Paris Mayor Anne Hidalgo had made a promise that from 2025, three sites where swimming had been prohibited since 1923 would reopen. 

In the past, Olympic swimmers have protested water quality in previous host countries. In 2016, swimmers protested the water quality in Guanabara Bay during the Rio Olympics. Likewise, swimmers ahead of the 2019 Tokyo Olympics complained that the water in Tokyo Bay was too polluted. 

Read more: 57 swimmers at triathlon championship fall ill; water quality blamed