Starting at the ornate Pont Alexandre III, the triathletes will swim in the Seine, cycle down the Champs-Elysees and Boulevard Saint-Germain before a fast, flat run taking in the Grand Palais and finishing on the same iconic bridge.

Organisers said the course was designed to "magnify" the sport but idiosyncrasies unique to Paris add more challenges to what is already one of the most gruelling events in the Games.

First, the Seine river.

Assuming the water is clean enough to race, the competitors will first have to swim with a strong current and then turn back to battle against it. Positioning will be key.

"I think a lot of people are anxious about the swim," Bermuda's Olympic champion Flora Duffy said. "That's something that, if you get it wrong, you can get it quite wrong."

On emerging from the Seine after the 1.5km swim, they must sprint up 32 time-worn stone steps to the bridge, where they swap swimming cap for helmets and jump onto bicycles.

The seven-lap, 40km cycling stage, though fast and flat, is also uniquely Parisian, with a quarter of the course on cobbled streets. That is all before the 10km run.

Along with the unknowns, the fact key contenders like Duffy and Tokyo silver medallist Georgia Taylor-Brown are returning from injury means nothing is a given in the women's race.

"There are probably six women that could win, or be on the podium, so it's very competitive and it's quite open, whereas in Tokyo it was more of a two-person race between myself and Georgia Taylor-Brown," said Duffy.

The men's race, scheduled a day after the women's race on July 31, is a little more predictable with Britain's Alex Yee and New Zealander Hayden Wilde the top contenders.

Yee said he was preparing for the cobbles and the current, mindful that the smallest things can make a difference on the day, but downplayed his status as favourite.

"For me, when I'm enjoying myself and when I'm most relaxed and not thinking about an outcome so much, I race my best," he said. "So I think that's the way I'm trying to frame this going into this Olympics."

FRENCH CHALLENGE

The eight-strong France team will be gunning for the country's first individual medal in the sport and looking to better the relay bronze they won in Tokyo three years ago.

The relay, a mixed-sex event scheduled for Aug. 5, is run over a much shorter course. Yee and Taylor-Brown helped Britain to win the title in Tokyo.

Cassandre Beaugrand was part of the France team in Tokyo and the 27-year-old can expect plenty of home support as she bids for an individual medal fresh off her first Olympic-distance race in the world series in Cagliari, Sardinia in May.

"The French athletes are all in form at the moment, they're a force to reckon with," said Britain's Beth Potter, who won the Olympic test event last August.

Norway's Kristian Blummenfelt, who will defend his Tokyo title in the men's race, has a plan for dealing with the noise from locals roaring on the French competitors.

"It will be important to turn that around to pretend they are cheering for you," he said.

The triathlon also marks the culmination of years of work to clean up the Seine, with Olympics organisers and Paris authorities setting the ultimate goal of a swimmable river for the public by next year.

At 4am on the morning of each of the three races, organisers, World Triathlon, race directors and medics will meet with the Paris water authority to discuss the latest test results and make a final call on whether the river is safe.

Those preparing for the Paris triathlon shrugged off the question.

"I think I've swum in much worse water, to be honest," said Taylor-Brown. "It's just the nature of the sport."