Paris mayor swims in Seine as river is cleaned up just in time for Olympics | Paris Olympic Games 2024

It has been the dream and promise of Paris mayors for decades and a nightmare for Olympic organisers: could the Seine be cleaned up enough to swim in and hold triathlon and other events?

For the last 100 years and up until a few days ago, the answer seemed to be no.

On Wednesday, however, the city’s mayor, Anne Hidalgo, kept her promise that it would be and she would be one of the first in. To cheers and applause, she led a group of about 10 officials, athletes and local people by donning a swimsuit and taking a dip in the river after a barrage of tests showed it was finally safe.

“It’s a dream day … and the sun is out,” Hidalgo said after performing a respectable crawl 100 metres downstream in water measured at 20C (68F). “It’s sweet and wonderful and the result of a lot of work. I remember at the very beginning in 2015 when we began our campaign for the Games, the international triathlon federation said why not a triathlon in the Seine? Will athletes be able to swim in the Seine? Today we can say they can.”

Tony Estanguet, the president of the Paris 2024 organising committee, congratulated city hall and the French authorities for making the river safe for swimming. “Today we have confirmation that the Seine is swimmable and that the triathlon and marathon swimming competitions can take place in it,” he said.

“As organisers we’re very happy to be able to offer athletes the best conditions … but over and above that what is at play is using the Games to speed up the transformation of the city and make it possible to swim in the Seine.”

He added that in the case of heavy rain, which could risk a spike in water pollution, contingency plans had been drawn up to postpone races for “a few days”.

Swimming in the Seine, which bisects Paris, has been banned since 1923 owing to health risks. In 1990, the then president, Jacques Chirac, promised to make it clean enough to swim in, but failed.

Hidalgo’s historic swim, which was postponed twice because of fluctuating pollution levels, came just 10 days before the opening of the Games on 26 July and after fears a large cleanup operation had failed. The work included the construction of a €1.4bn (£1.2bn) holding and treatment tank to contain bacteria-laden stormwater during heavy rains, which came into operation a month ago, and improvements to the city’s wastewater network.

Until very recently, the river was still failing water quality tests for E coli bacteria– an indicator of faecal matter – and showing levels above the upper limits imposed by sports federations.

Triathlon events will be held on 30, 31 July and 5 August, and a swimming marathon on 8 and 9 August. The paratriathlon will take place on 1 and 2 September.

Competitors in the open-water swimming events and triathlon will set off at Pont Alexandre III, a marvel of 19th-century engineering near the foot of the Champs-Élysées, with the Eiffel Tower in the background.

The water will be tested regularly at several points before each event and authorities are certain it will be clean with 75% of identified bacterial pollution eliminated.

Paris Olympic organisers have said that if heavy rain during the Games affects pollution levels in the river, the triathlon would no longer feature the swimming portion – and the marathon swimming competition would be relocated.

As another sign of hope, French experts have identified more than 30 species of fish in the Seine in Paris, compared with three in 1970.

After her swim, Hidalgo said making the Seine swimmable would also help the city adapt to the climate crisis and mitigate the pollution of the ocean into which the river flows.