PARIS — Worries about water quality forced the cancellation of another Paris Olympics test event in the Seine River on Sunday, as organizers called off a triathlon mixed relay.

While triathlon swimmers took to the Seine in competition on Thursday and Friday, water quality tests showed higher than authorized levels of bacteria ahead of a para-triathlon test event Saturday, so it was canceled. Further tests ahead of Sunday's mixed relay remained inconsistent, according to a joint statement from organizers and local officials.

“As a precautionary measure and to protect the health of the athletes, the decision has once again been taken to cancel all the swimming races scheduled for today,” it said. Authorities are investigating the reason for the problematic tests.

Rainfall in recent days may have been a factor. A previous test event had to be canceled this month because heavy rain caused overflows of untreated waste into the Seine, leaving water quality below safety standards.

The cancellations this weekend pose a new challenge to the Paris Olympics organizers and the city’s ambitions to reopen the iconic river to public swimming after the Games.

Paris is spending massively on water-management projects that officials say will make pollution caused by storms less frequent by the time the Games begin on July 26, 2024. Olympics organizers remain determined to hold open-air swimming events along the picturesque river, viewing this month’s cancellations as a learning experience. — Euronews