Forget Olympic athletes — will Parisians ever want to swim in the Seine?

PARIS — In the minds of French officials, the plan was ambitious but simple: Clean up the Seine for the 2024 Olympics and convince the world that everyone could enjoy a carefree dip in the notoriously murky river next summer.
Well, Olympic athletes did ultimately swim in the Seine, even if they raced through a squall of doubts, delays, illnesses and dark jesting about what they saw along the way.
But locals might not be so eager to jump in.
It’s not that the goal isn’t admirable, water quality specialists studying the Seine told POLITICO. They all agree that cleansing the Seine is long overdue — and is happening. But they have lots of questions about how trustworthy the tests proving the Seine is “safe” are, and they’re wary about what the existing data reveals. 
“All you have to do is look at the data for the [past] four years to answer ‘no,’” said Jean-Marie Mouchel, a professor at Sorbonne University who is part of a group of scientists studying pollution levels in the Seine.
“It seems [water] quality is improving, though probably less fast than the decision makers who launched all this work had hoped,” he added. 
Yet Paris Mayor Anne Hidalgo is insisting it’s one step down, one to go. Full steam ahead. The longtime Socialist mayor, who has banked her political career on turning the French capital into a greener city, dismissed claims that the Seine was unsafe for swimming as “fake news” that were “destroying everything [including] trust between people.” 
The outcome next summer will serve as a high-profile verdict on whether cities can, in fact, rapidly scrub rivers that have suffered centuries as urban dumping grounds. Paris is far from the only city trying to accomplish in short order what has eluded big city officials for decades. London, New York, Chicago — pick any major metropolis and similar efforts are underway. 
Hidalgo first promised to make the Seine swimmable for all eight years ago. Since then, the undertaking has cost the French authorities €1.4 billion for the titanic infrastructure projects involved. 
These include a giant underground pool to store sewage water and prevent it from spilling into the river, disinfection systems to treat the water coming out of two treatment plants upstream from Paris, and a system redirecting wastewater from more than 10,000 homes that used to dump into the Seine.
The facilities were built just in time for the Olympics, but may not be enough to allow Hidalgo to deliver on her promise.
To get there, she’ll have to get the Seine up to EU standards on public bathing spots, which require E. coli bacteria levels below 900 colony-forming units (cfu) per 100 milliliters of water in at least 90 percent of samples.
E. coli is a common standard used to check whether water has recently been polluted by fecal particles. The bacteria’s presence can cause mild illnesses and is primarily associated with symptoms like vomiting or diarrhea. 
Under EU law, public bathing in a new spot is allowed only if bacteria concentrations remain under the limit for four years in a row, with testing taking place several times a year.
But there’s a caveat: The measurements taken during certain weather events during which it’s impossible to swim can be excluded from the monitoring process. According to Mouchel, the Sorbonne University professor, that criterion is open to interpretation – to some extent.  
Since regular testing began in the Seine in 2016, there have been several floods upstream from Paris — most recently this summer, in the Marne River, one of the Seine’s main tributaries.
The city of Paris is planning to allow swimming only during the summer, meaning measurements taken in the winter time — when heavy rain and storms are more likely — might not be taken into account. But according to Mouchel, the professor studying the Seine, EU regulation isn’t clear on whether data from periods when swimming is prohibited can be excluded or not. 
Water-quality specialists also take issue with the regulation and standard methods of testing to begin with. 
“They are completely inadequate for actually measuring risk in a river like the Seine,” said Dan Angelescu, the CEO of Fluidion, a startup that specializes in monitoring water quality based in Alfortville, on the periphery of Paris. 
The firm says it has a new, more precise testing method. To do this, it measures both free-floating bacteria and bacteria attached to other particles. The standard procedure approved and used to comply with EU regulations does not factor in all of the attached bacteria.
Fluidion carried out its own tests during the Olympics, and found that the results using this new scheme were “much, much higher” than the official tests, Angelescu said.
The company has been sharing its data with the city of Paris, which signed Fluidion to a water-monitoring contract in 2017. The city chose to stick with the standard measuring methods for the Olympics, however. 
“I cannot blame them,” Angelescu said, adding that it was understandable for the city of Paris to stick with the approved testing method under the current regulation. But he argued this method, “can provide an overly optimistic picture of water quality and undercount E. coli and the associated risk in waters that contain [fecal] particles.”
Scientists say Fluidion’s findings — summarized in an article that was published on the day of the Olympic triathlon race but has yet to be peer-reviewed — are interesting. But they’re not bulletproof, either.
The regulatory test only measures the number of viable bacteria — the ones that could make you sick — from a given sample that can grow and multiply in a laboratory environment, which takes between 18 and 24 hours.
Fluidion’s method uses a portable measuring device. That allows for quicker results, within a few hours even.
But assessing whether a river is clean enough to swim in isn’t all about speed. In fact, existing research looking at how exposure to certain bacteria can cause diseases relied on the slower, standard method.
This means there’s no way to assess the sanitary implications of a higher comprehensive count of E. coli, said Françoise Lucas, a professor at Paris-Est Créteil University.
“Wanting to know the true bacteria concentration is an illusion,” Lucas said. “There’s no ideal method, they all have their own biases.”
Then there’s the issue with the EU standards themselves. 
“Overall, we [the EU] are more lenient than in other countries,” said Mouchel, the professor studying the Seine. 
The current EU framework was adopted in 2006 and was set for an update in early 2023. That hasn’t happened yet. 
Some NGOs and lawmakers working on the subject say the 2006 standards are outdated, as they do not account for other types of pollution from microplastics or chemicals. 
“Europe must play its role of supervisor and protector, not only against microbiological pollution but also chemical pollution,” European Parliament lawmaker Yvan Verougstraete, with the centrist Renew Europe group, said in a statement during the Olympics. 
Yet updates would require the EU to reassess all its beaches, swimming holes and lakeside lounging spots — and go after any that no longer comply. 
“Then it’s a political question of how many beaches we want to shut down,” Mouchel said. “That’s another story.”
Beyond the scientific debates, everyone agrees the Seine’s swimming saga has prompted much-needed infrastructure investments that will benefit the public whether swimming starts next year or not. 
Just since the city’s new wastewater basins began working in June, the river has already seen massive improvements in quality. And maybe now, people will think twice about tossing that cigarette butt on the street, knowing it often will end up in the Seine. 
“Without ambition, you don’t do anything,” Mouchel said — but that doesn’t mean skeptics will soon be dipping their toes in the water. 
“When our data will say that we can swim, I will,” said Angelescu, the Fluidion CEO.
Giovanna Coi contributed reporting for this piece.