Swimming in the Seine, the great challenge of the 2024 Olympic Games

Olympic freestyle and triathlon events with the Eiffel Tower, the Grand Palais or the golden horses of the Alexandre-III bridge as their backdrop… It is to capture these prestigious images that the French organizers of the JOP (Olympic and Paralympics) of 2024 have promised that the Seine will be made swimmable for the athletes. “A commitment held by the State” headlined a press kit from the prefecture of the Île-de-France region in early July. But since then, several cancellations of events considered to be pre-Olympic tests have cast doubt. On August 6, participants in the World Freestyle Championship were unable to compete in water that had become too polluted following several days of heavy rain. Fifteen days later, in great weather this time, triathlon events also had to be canceled. In question, according to the City of Paris, “the malfunction of a valve of a sewerage network”. Will the water of the Seine really be ready for the athletes?

“The bathing plan, with 1.4 billion euros of investment, continues to progress. All the works planned to improve water quality will be delivered during the first half of 2024”, assured Pierre Rabadan in early August. , deputy mayor of Paris in charge of sports. In fact, very significant funding has been mobilized since the creation in 2019 of a “task force” (operational force) placed under the aegis of the prefecture. It brings together all the partners involved in the challenge of making the Seine compliant with the standards required for taking a dip: Water Agency, sanitation professionals, local authorities, river ports, etc.

Major works

“Taking care of a river requires good territorial coordination between upstream and downstream, underlines Françoise Lucas, microbiologist at the Leesu laboratory (Paris-Est-Créteil University). Coupled with very significant resources, this collective work will continue to improve water quality.” Two major wastewater treatment plants located upstream of Paris (Noisy-le-Grand and Valenton) were modernized in 2023 to reduce faecal contamination discharges, key indicators for bathing standards. The ports that accommodate stationary barges, from Paris to Val-de-Marne, have been equipped with networks to collect their wastewater. Half of the boats would already be connected, according to the prefecture.

In order to ensure bathing at least in dry weather, a major challenge concerns the fight to remedy 23,000 “bad connections”: formidable waste water discharges into rainwater networks, which end up without any depollution in the river. Exceptional financial aid has been put in place to put an end to it, but the rest to be borne remains significant for the individuals concerned… The Île-de-France prefecture estimates that “a quarter of these connections have already made the subject to upgrading, and that another quarter will be by the 2024 Olympics”. According to Michel Riottot, who follows the bathing plan within the France Nature Environnement Île-de-France association, the account will not be there. “Correcting the existing one requires thousands of euros that many individuals are not ready to pay. If in the summer of 2024 there are still more than 10,000 bad connections, it will be a problem. Difficult to catch up in a short time a century of bad practices consisting of dumping our effluents directly into the Seine!”

At the mercy of the weather

But like our ancestors the Gauls, the organizers of the 2024 Olympics fear above all that the sky will fall on their heads… in the form of rain. In Paris, where the ground is very waterproof, runoff water can quickly overflow the sewerage networks into the Seine. And that’s not all: “In town, the rains carry the faeces of domestic animals and birds. In Seine-et-Marne, upstream of Paris, they can also wash the manure present into the river and its tributaries. on agricultural land”, explains Françoise Lucas.

To reduce the risks, several major works are under construction: a 50,000 m 3 storm basin near the Gare d’Austerlitz, a 9 km pipeline south of Paris, a rainwater pollution control station in Val-de-Marne, etc. Will they be sufficient if an exceptional rainy event occurs in the days preceding the freestyle and triathlon events on August 8 and 9, 2024? Anyway, the very expensive efforts to clean up the Seine should at least serve to refresh Parisians from the summer of 2025, when three bathing places will (normally) be open to them. After a hundred and two years of prohibition.