Paris 2024 organisers cancelled training for open water swimming on Tuesday because of pollution in the River Seine.
It is the fifth time the water quality has forced a swim familiarisation session to be cancelled during these Games, while the men's race also had to be put back a day.
The latest cancellation comes a day after triathlon's mixed team relay was held.
All the triathlon swim legs have taken place in the Seine, which is also set to be used for marathon swimming.
Tests showed the levels of the enterococci bacteria in the water had dropped back below the required standard, although E. coli levels were still deemed acceptable.
Another familiarisation session is scheduled for Wednesday, with the women's 10km race due to take place on Thursday and the men's race on Friday.
World Aquatics spokesperson Anne Descamps said: "We are confident the events will go ahead as planned given the weather tendency."
Heavy rainfall has increased the levels of bacteria in the Seine, although hot weather helps to reduce the count.
If the Seine is still deemed unsuitable, organisers said marathon swimming can be moved to Vaires-sur-Marne, east of Paris, where the rowing and canoeing competitions take place.--BBC
