At the end of May, when Anne Hidalgo and Emmanuel Macron announced that they would dive into the Seine on June 23, social networks went crazy. On X (formerly Twitter), #JeChieDansLaSeineLe23June quickly became the most shared hashtag, riding a wave of more or less subtle mockery.
However, when we look at the merits of the subject, there is no reason to worry (even if the inaugural dive has just been postponed due to the flow of the river). Yes, the Seine will be swimmable for the triathlon, paratriathlon and marathon swimming events this summer.
“This is not a subject for us”, immediately decides Dorian Coninx, French triathlon world champion, annoyed by this question. “We know that everything has been put in place to ensure that the Seine is clean this summer, and then for the population in the future. It is a source of pride to bring this heritage of a swimmable Seine to Parisians.”, adds Benjamin Maze, DTN of French triathletes. “The skepticism is that of the public, not of the athletes.” note for his part Pierre Rabadan, deputy for Sports and the Olympic and Paralympic Games at Paris town hall.
“We don’t have a plan B for the triathlon, because there’s no need for one. At worst, we can postpone the competition in the event of a storm, but the Seine will be swimmable, that’s for sure.”
Pierre Rabadan, deputy for Sports at Paris town hallat franceinfo: sport
Tired of the mockery, Pierre Rabadan draws a parallel with the pedestrianization of riverside roads in 2018: “Everyone made fun of the mayor of Paris. Today, if we wanted to go back on this, the same people would say we were crazy. This reconquest of the Seine was a virulent fight.. But a fight which is bearing fruit, with today 35 species of fish in the Seine, which there were only three in the 1980s.
“The swimming plan is the last piece of this reconquest, since it will return the Seine to Parisians from the summer of 2025slips Pierre Rabadan. Thanks to the Olympics, we gained 15 years on this 1.4 billion euro project.” Because to allow athletes, then Parisians, to swim in the river, we had to invest, and not just within the walls. “For the Seine to be swimmable at the Alexandre III bridge, it must enter Paris clean, and it must remain clean. And that happens well in advance.”summarizes Samuel Colin Canivez, chief engineer of the Austerlitz basin, one of the buildings constructed as part of the swimming plan.
“The swimming plan involves around thirty communities, it costs 1.4 billion euros. It involves all the territories linked to the Seine and the Marne”
Samuel Colin Canivez, engineer responsible for major works on the Parisian sanitation networkat franceinfo: sport
Concretely, to make the Seine swimmable for the Games (and after), it was necessary to act on several areas. “The 255 boats and accommodations on the Seine are now all connected to a port. Their wastewater now goes into the sewers, which was not the case before.”argues Pierre Rabadan, who adds: “We also counted 20,000 homes which discharged, consciously or not, their wastewater into the Seine and the Marne upstream of Paris. Half was reconnected correctly.”
Still upstream of the capital, a river water depollution station was inaugurated at the end of May, in Champigny-sur-Marne. But the heart of this project are the pools built around and in Paris, like the Austerlitz pool, the “star” of this swimming plan. “Basically, it’s a waiting room for rainwater to avoid saturation of the sewers, while waiting for this water to be treated and then discharged.”, explains Samuel Colin Canivez. “Today we can store 100,000 m3 more in Paris.”
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This set of comparable basins was therefore created to counter the main source of pollution of the Seine: domestic wastewater. “What pollutes the water with bacteria is the toilet flushes that end up in the Seine.”, simplifies the engineer. He pursues : “By checking the connections and connecting the boats, we limited these wastewater spills during dry weather: that was the first step.”. It remained to resolve the problem of rainy episodes.
“When it rains too much, the sewers become saturated. To prevent it from overflowing into the public square, we use the natural environment that we have on hand if we do not have a flow regulation system”
Samuel Colin Canivezat franceinfo: sport
However, all storage basins fulfill this role of flow regulation system. Their goal is simple: to ensure that no wastewater is dumped into the Seine, even in the event of heavy rain. “There will always be weather events that exceed the capacity of infrastructurehowever, warns Samuel Colin Canivez. We flush three million toilets per day in a few square kilometers in Paris. In addition to this, the flow of the Seine is very low, which makes it very vulnerable to pollution.”
Despite all these efforts, the NGO Surfrider – which has been taking regular samples since September 2023 – “was alarmed” by the state of the waters of the Seine at the beginning of April. “Which didn’t mean anything, since everything that was built came into service there, at the beginning of June”, sweeps Pierre Rabadan, at Paris town hall. Moreover, Marc Valmassoni, hydrogeologist, admits: “On paper, we are very favorable to what has been done. We can only be delighted that the arrangements have been put in place. Now, we are awaiting the full commissioning of all the equipment to see the concrete effects.”
If we “wait to see all this in operation before judging” at Surfrider, Marc Valmassoni is anything but skeptical. The hydrogeologist, however, regrets that Paris town hall has focused solely on rain: “They have not worked on the de-waterproofing and revegetation of the soil. A drop of water that falls on the concrete is loaded with materials and bacteria, whereas if it falls on earth, it enriches the soil without load.”
Despite everything, the time has come for optimism in all camps, far from the bad memories of test events canceled in summer 2023. “These cancellations allowed us to detect oversights. On the day of the triathlon, for example, we had an electronic failure, a valve appeared closed even though it was open. This allowed us to set up a monitoring system. monitoring of the underground network much more meticulous”explains Pierre Rabadan.
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Like many at Paris City Hall, the Sports Deputy hopes that the storm has passed. “Now, people will understand that all this goes beyond the Games. From 2025, we will have three swimming sites in Paris at Bercy, Grenelle and in the Marie arm. And we have already had 27 requests to open swimming elsewhere than in Paris”assures the elected official, who already imagines organizing competitions for the general public, in the Seine.
A success welcomed by the NGO Surfrider. “It’s going to get hotter and hotter, people are going to need access to cool air, so swimmability in the city is a key issue”, appreciates Marc Valmassoni. Enough to make Pierre Rabadan a bit teasing: “Anyone who makes fun of this swimming plan, I’m sure we’ll see them in swimsuits soon…”