Athletes jump into the Seine from the Alexander III bridge at the start of the first stage of the women’s triathlon trial at the Paris 2024 Olympics in Paris in August 2023.
Michel Euler/AP
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Michel Euler/AP
PARIS — With Paris Olympics With less than two weeks to go, a question looms for the Olympics: Will the Seine be clean enough for athletes to swim in?
The triathlon and marathon swim are scheduled to take place on the Seine, where swimming has been illegal for more than a century. Despite the city’s efforts to clean up long-term polluted riverThe water has been tested unsafe for human consumption in recent weeks and cleaner on other days. The Olympics run from July 26 to August 11.
To clean up the river, Paris has invested 1.4 billion euros ($1.5 billion) in building infrastructure to collect more rainwater when it rains — the same water that contains bacteria-laden wastewater that flows into the river during heavy rains and makes it unsafe to swim.
In May, Paris officials inaugurated a giant underground water tank next to Austerlitz train station that will collect excess rainwater and prevent sewage from flowing into the Seine. The tank, which can hold the equivalent of 20 Olympic swimming pools of dirty water, will now be treated and is at the heart of major infrastructure improvements the city has rushed to complete in time for the Olympics, but also to ensure Parisians have a cleaner Seine for years to come.
But a few heavy rains could push E. coli levels above the 900 colony-forming units per 100 milliliters limit that the World Triathlon Union has determined is safe for competition.
“The Seine is not a special case,” said Metin Duran, a professor of civil and environmental engineering at Villanova University who studies stormwater management. “It’s a really complex and expensive problem.”
Paris, like many other ancient cities around the world, has a combined sewer system, meaning that the city’s wastewater and rainwater run off through the same pipes. During heavy or prolonged rainfall, the pipes reach their maximum capacity, meaning raw sewage flows into rivers instead of treatment plants.
The Eau de Paris monitoring group has been testing the river water daily and released results showing unsafe levels of E. coli in recent weeks, followed by results in early July showing improvement.
Paris Olympic organisers have said that if heavy rain affects the flow of the Seine during the Games, the triathlon will no longer have a swimming component – and the marathon swim will be moved to the Vaires-sur-Marne Marine Stadium in the greater Paris region.
“It’s not very common, but it has happened a few times,” Ollala Cernuda, communications director at World Triathlon, the sport’s international organization, said of the possibility of the swim being canceled.
“And it always comes down to water quality issues,” Cernuda said.
But organizers remain optimistic that drier, sunnier weather than the French capital experienced in June will allow the events to go ahead as planned — helped by infrastructure upgrades. The sun’s ultraviolet rays kill bacteria like E. coli in the water.
An AP analysis of weather data found that in 2024, Paris was the city with the second-most rainiest days since 1950, behind only 2016.
It is important for the water quality of the Seine that there are very few days without rain.
According to the analysis, Paris has only experienced one dry week this year – in early June, while from 1950 to 2020, the city usually had at least three such dry spells by the end of June.
“Precipitation predictions have become much more accurate a week in advance,” said Jennifer Francis, a scientist at the Woodwell Climate Research Center in Massachusetts. “But seasonal models from decades ago no longer provide reliable guidance in our warmer world.”
As the Olympics approach, the heated debate over the cleanliness of the Seine River has become a source of frustration for some athletes like Léonie Périault, a French triathlete who won a bronze medal at the 2020 Tokyo Olympics.
“Every time I meet someone, they are worried that I will swim in the Seine,” Périault said. “But I have been swimming in this river for many years now. In junior competitions, we swim in the Seine regularly and have never had any problems.”
Last year, Périault took part in a test event on the Seine.
“The setting is amazing with the Eiffel Tower in the background and the water conditions are no worse than anywhere else in the world,” she said.
On Saturday, French Sports Minister Amélie Oudéa-Castéra dove into the water to prove the famous river was clean enough. Paris Mayor Anne Hidalgo also said she would swim in the Seine this week.
Dan Angelescu, founder and CEO of Fluidion, a water monitoring technology company based in Paris and Los Angeles, said there have been improvements observed in the river since the city’s new infrastructure came online, but the Seine’s water quality remains fragile. His company has been measuring pollution levels in the Seine for years.
It’s hard to predict, based on data from previous years, what might happen later this month, Angelescu said — since water tanks and other infrastructure weren’t operational until a few months ago.
“It’s hard to say,” Angelescu said in early July after the Seine water was found to be cleaner than it had been a few weeks earlier.
“Seeing such a strong and rapid improvement could be a sign that something is working,” he said.
