But poor water quality forced the cancellation of three test swimming events in July and August last year, and local authorities still have thousands of new sewer connections and vital stormwater infrastructure to complete in the coming months.

Paris Mayor Anne Hidalgo pledged on Wednesday to take a "historic dip" in the Seine before the Games begin to highlight what she sees as a key part of the city's Olympic legacy: the creation of three open-air swimming pools for the public.

"Everyone said it was impossible and we've done it," she told reporters at the City Hall. "We are going to swim in the Seine," she declared in her New Year's address at the Hôtel de Ville, inviting the regional prefect, Marc Guillaume, to join her in this "historic dip", "more than 30 years after Jacques Chirac's promise".

The former president, then mayor of Paris, had promised in 1990 to "bathe in the Seine in front of witnesses" in 1993, but never kept his promise.

In July 2023, she announced the opening of three public bathing areas in the capital for the summer of 2025, in Bercy, Grenelle and between Île Saint-Louis and the Marais. 

To mark the occasion, her deputies for urban planning, Emmanuel Grégoire, and for sport, Pierre Rabadan, jumped into the water themselves, something the socialist mayor did not do. 

Swimming in the Seine, which had already been practised under the Ancien Régime, had been banned in Paris by a prefectural decree a century earlier, in 1923 

Since then, a river brigade has been on constant patrol to prevent diving. But for the Olympic Games, swimming will be reunited with the Seine: the triathlon and open water swimming events will start from the Alexandre III bridge, which links the Grand Palais to the Invalides.

But it was during these test events that the organisers of the Paris Olympic Games suffered some serious setbacks last summer. Before the cancellation of the two triathlon events, Para and Mixed, it was the open water swimming events that had to be cancelled due to pollution caused by an unusually heavy summer downpour.

Thomas Bach, President of the International Olympic Committee, said he is "confident" and "optimistic" about these events and assured us that "by the time we get to the Olympics, it will be a great success that will benefit the entire population".

Since 2016, the state and local authorities in the Paris region have invested around €1.4 billion to make the Seine and its main tributary, the Marne, swimmable.