The World Triathlon Para Cup in Paris had the swimming stage cancelled on Saturday due to poor water quality in the River Seine as organisers said they could not risk the health and safety of athletes.
Earlier this month, organisers also cancelled the Open Water Swimming World Cup in Paris after heavy rainfall caused the water quality in the river to dip below minimum health standards.
Water quality tests were conducted early on Saturday, after which organisers took the call to switch the Para triathlon competition to a duathlon format.
"We have observed a significant discrepancy on the data between the results of the latest water quality tests provided by the laboratory and the high frequency sample analysers," World Triathlon said in a statement.
"Considering this discrepancy, and not to put the health and safety of the athletes at risk, the decision has been made to cancel all the swim activities planned for today."
The city has been working on clean-up efforts to make the Seine swimmable again, as it was during the 1900 Paris Olympics more than a century ago.
But heavy rain causes the Parisian sewage system to overflow and be discharged into the river.
Triathlon fan Vincent Corla was hopeful the Games events would go ahead as planned next summer.
"Triathletes are used to swimming in places worse than the Seine. Sometimes, when we're in the water, we don't even see our hands anymore under water. So for me, it doesn't shock me at all.
"I hope next year at the real Olympic Games it won't turn into a duathlon, that it will be a great event."
The women's and men's Olympic test events took place on Thursday and Friday, respectively, with Beth Potter and Alex Yee winning gold to complete a British double.
