Findings of an investigation by public authorities pointed to an incorrectly closed sewer valve in the eastern Tolbiac district, upstream from the historic Alexandre Bridge where the event should have taken place on the weekend, a council spokesperson said.

Le Canard Enchaine and Le Parisien newspapers first reported the news.

The swimming stage of the World Triathlon Para Cup - seen as a test event for the 2024 Summer Games - was cancelled on Saturday due to poor water quality.

Athletes had taken part in swimming events in the Seine on the previous two days.

"The valve that prevents rainwater from being discharged into the River Seine appears to have leaked," Sports Minister Amelie Oudea-Castera was quoted as saying by Le Parisien.

Paris has been working on cleaning up the Seine so that people can swim in it again, as was the case during the 1900 Paris Olympics more than a century ago.

"Next year, two major rainwater retention facilities will be brought into service, which will greatly reduce the impact of rainy weather", the Paris spokesperson said in a statement.