Even before he has dipped his toes into the murky waters of Paris’ famous but forbidden River Seine, French triathlete Thibaut Rigaudeau is already fielding questions from disbelieving friends.

“Are you scared of swimming in the Seine?” he says they ask him. “It looks disgusting.’”

For decades, it was. Though immortalized in art, literature and song, and cherished by lovers who whisper sweet nothings or tearfully part on the privacy of its banks, the river was ecologically dying.

It was too toxic for most fish and for swimmers, largely useful only as a waterway for goods and people or as a watery grave for discarded bicycles and other trash. Swimming in the Seine has, with some exceptions, been off-limits since 1923.

Now, however, its admittedly unappetizing green-brown waters hide a tale of rebirth.

A costly and complex cleanup is resuscitating the Seine just in time for it to play a starring role in the 2024 Paris Olympics and, after that, for it to genuinely live up to its billing as the world’s most romantic river, one that’s actually fit again for people. And in a warming world, a renewed ability to take cooling dips in the river should help France’s capital remain liveable during increasingly frequent heat waves. It possibly might also inspire other cities to invest in reclaiming their waterways.

“It will create waves, so to speak, across the world because a lot of cities are watching Paris,” says Dan Angelescu, a scientist who is tracking the Seine’s water quality for City Hall, with regular sampling.

“It’s the beginning of a movement,” he says. “We hope so, at least.”

The Olympic deadline has supercharged a cleanup that has been decades in the making. Without the imperative of having to be ready for 10,500 Olympians in July and August next year, followed by 4,400 Paralympians, City Hall officials say it would have taken many more years to fund the multi-pronged, 1.4 billion-euro ($1.5 billion) effort.

Because as well as hosting outdoor swim races, the Seine is going to be the centrepiece of Paris’ unprecedented Olympic opening ceremony. For the first time, it will take place not in a stadium setting but along the river and its banks.

So it needs to be ready. Officials have been going after homes upstream of Paris and houseboats on the Seine that were emptying their sewage and wastewater directly into the river. An Olympic law adopted in 2018 gave moored boats two years to hook up to Paris’ sewage network.

City Hall says samples taken daily last July and August in the stretch of river where Olympians and Paralympians will compete showed the water quality was overwhelmingly “good.” By their sports’ standards, that means acceptable.

Officials hope Parisians will start to feel that it’s safe to go back in the water when they see Olympians and Paralympians leading the way.