A first life-size test on the swimmability of the Seine. This weekend, a swimming event must take place in the Parisian river. Saturday swimmers and Sunday swimmers will crawl 10 kilometers from 7:30 a.m. to 10 a.m., completing several 1.6 km loops between the Alexandre III bridge and the Alma bridge, with the Eiffel Tower in the background.

But the rain could derail the event. The heavy rains that have fallen in recent days could pollute the river and prevent the competition, the first pre-Olympic swimming race, from taking place.

This is a frequent phenomenon, especially on the coasts. Faced with a sudden and large influx of water to be treated, treatment plants saturate and overflow, releasing untreated wastewater. Result on the beaches, a purple flag is hoisted, prohibiting swimming due to pollution. Now the problem arises in Paris, a few days before a swimming test in the Seine.

Because it is indeed intense rains that could spoil the sports festival, which bring wastewater back into the river, causing the sewers to overflow. After several days of rain in Île-de-France, and more rain this Friday, will the analyzes be good? Doubts arise. “There is a risk”, abounds one of the authorities concerned while waiting for the latest results of analyzes carried out by Eaux de Paris.

Last Thursday, the prefecture of the Île-de-France region, on the basis of the 42 bacteriological analyzes of June and July, had authorized “in principle” the swimming events in open water which must be held on Saturday and Sunday, as well as those of the triathlon from August 17 to 20. This weekend, it is precisely a World Cup open water swimming event organized under the aegis of World Aquatics, the international swimming federation.

“If there is no improvement in the weather, it will be complicated,” conceded one of the authorities concerned on Tuesday. Because between Eaux de Paris, the organizing committee of the Olympics, the town hall of Paris, the prefecture of Île-de-France…, many are looking at the results of water analyzes, which must respect the required standards. by the international federation. The famous bacterium Escherichia coli and enterococci are particularly tracked.

On June 9, the daily analyzes, on the basis of the European regulations in force, had given “excellent results”, had rejoiced the town hall of Paris. But, recognized Pierre Rabadan, deputy for sport and the Seine at the town hall, “if it rains torrents for a week, it will be complicated”. The readings for the summer of 2022 – “before all work in progress” – were 92% satisfactory to authorize swimming, he recalled at the time.

Especially since all the sites allowing the absorption of this river water have not been completed, in particular the Austerlitz basin, still under construction, which will make it possible to store rainwater (50,000 m3) from the start of 2024.

The training session scheduled for Friday morning for the event has already been canceled. “Following recent heavy rains in Paris, the water quality of the Seine is currently below acceptable standards for safeguarding swimmers’ health,” the French Swimming Federation (FFN) said in a statement. . The decision to “cancel” this training was made in concert with the international federation World Aquatics and “public health partners”.

At this point, only the workout is cancelled. The holding of the World Cup event, the women on Saturday and the men on Sunday, will depend in particular on the latest water analyzes (24 hours before each time) and the weather forecast.

For the Olympic Games in 2024, the organizers have long planned to be able to postpone the events by two or three days, in the event of storms and heavy rain. This first test is a premise for future swimming promised for 2025 by the mayor of Paris, Anne Hidalgo, on three sites while swimming has been prohibited there since 1923.

From 2025, we will be able to swim in the Seine thanks to the Games! The 3 bathing sites in the Seine retained: Bras Marie (Paris Centre), Grenelle (15th) and Bercy (12th). My assistants have already taken a first dive! It will soon be your turn and also mine ?? pic.twitter.com/Hh2dGxSgPF

Since 2016, the State and local authorities have spent approximately 1.4 billion euros on all projects intended to make the Seine bathable (correction of evacuations of houses and barges, modernization of purification plants, construction of storage and sanitation stations, etc.) and thus prevent rainwater from carrying wastewater into the river.