Poor water quality in the River Seine has forced a cancellation of swim training for Olympic triathletes.

But top Australian medal chance Matt Hauser had predicted the day before that might happen and organisers remain confident the racing will go ahead as planned.

A familiarisation swim session planned for 8am Sunday (local time) was cancelled, despite sunny conditions.

Holding the swim legs of the triathlon events and the marathon swimming in the Seine has become a major Paris Games story.

The persistent rain that marred Friday night's opening ceremony along the famed waterway and continued into Saturday is the nightmare scenario for the event.

It raises water pollution, a nagging issue for the triathlon and marathon swimming events.

But the Australians made it clear if it was up to them, the 1.5km swim will go ahead at next week's events no matter how bad the water conditions.

Asked if he would swim in the Seine on Saturday, despite the weather, Australia's top medal contender Hauser said "bloody oath I would".

"We're expecting a triathlon. It's good to go at this stage. Swim familiarisation might not go ahead tomorrow, just for the safety of the athletes," Hauser said on Saturday.

"It's going to be a true test of an Olympic champion. It's got to be a triathlon.

"All the signs are showing that it is going to be a triathlon, which is great."

The men's triathlon is scheduled for Tuesday, with the women taking on the same 1.5k swim, 40km bike and 10km run in the heart of Paris the following day.

The mixed team relay, also featuring the Seine, is set for August 5.

Organisers could change the triathlon to a bike-run duathlon and move the marathon swimming to the rowing venue.

"(That) will be a big shame, but we really believe it's going to be a triathlon," Hauser said.

Organisers have spent more than one billion euros on the Seine river quality as one of the Games' big legacy projects.

But the levels of harmful bacteria in the water are still affected by the weather.

"The tests carried out in the Seine yesterday revealed water quality levels that in the view of the international federation, World Triathlon, did not provide sufficient guarantees to allow the event to be held," event organisers said in a statement.

"This is due to rain that has fallen on Paris on 26 and 27 July. Given the weather forecast for the next 48 hours, Paris 2024 and World Triathlon are confident that water quality will return to below limits before the start of the triathlon competitions.

"As observed in July, with summer conditions, water quality in the Seine has improved significantly. Paris 2024 and World Triathlon reiterates that the priority is the health of the athletes."

The bike and running familiarisation sessions on Sunday went ahead as planned.