Estimated to have cost a whopping $1.5 billion, the cleanup of the Seine river that flows through Paris is among the costliest projects the city has undertaken as it gears to host Summer Olympics for the third time.  

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Paris Mayor Anne Hidalgo on Wednesday jumped into the Seine in the city to prove that it is clean enough for open water swimming events at the 2024 Paris Olympics, scheduled to start on July 26. 

Ms. Hidalgo jumped into the river wearing a wetsuit and goggles, to showcase the river’s cleanliness as Paris gears up to host the international sporting event. 

BBC journalist Hugh Schofield followed, but without a wetsuit. Gulping a mouthful of the river water as he jumped in, Mr. Schofield said, “It tastes fine.”

“Water’s gorgeous…a bit murky. But, it feels good,” he said.

Seine, the lifeline of Paris

A sentiment that has echoed through art, literature, and pop culture is that Paris is a river city. “The evolution of Paris and its history can be seen from the River Seine,” UNESCO’s World Heritage Conservation notes. Over centuries and ages of development, sites and monuments that have been built on the banks of the Seine have come to define Paris – from the Cathedral of Notre-Dame and the Sainte Chapelle in the Middle Ages, to Pont Neuf during the French Renaissance, from the Marais and the Ile-Saint-Louis neighbourhoods of 17th and 18th centuries, to the Palais de Louvre, the Invalides, the Monnaie, and the most famous of all – the Eiffel Tower.

From Midnight in Paris (2011): Gil (Owen Wilson) and Gabrielle (Léa Seydoux) walk on the Pont Alexandre III bridge over the Seine.

Today, you can take boat rides on the Seine to explore the landmarks on the river’s banks. You may recall the one Jesse (Ethan Hawke) and Celine (Julie Delpy) took in Richard Linklater’s 2004 movie Before Sunset.

Touring companies facilitate all kinds of boat rides – from modest ones to fancy, luxurious yacht rides on the Seine. In 2024, Uber launched a private summer cruise on the Seine for free in partnership with Click&Boat, a leading boat rental company in Europe The one-hour cruise will be available from July 12 to 18 and again from July 28 to August 3.

Organisers of the 2024 Paris Olympics have aimed at linking most of the city’s iconic venues with the theme of a “celebration along the Seine.”

The Olympic bid

Cleaning up the Seine formed a crucial part of Paris’ bid for the 2024 Olympics.

The official bid said that Paris was “committed to use the Games as a catalyst to achieve a centuries-old dream of public swimming in the river – one that continues to resonate strongly in the French imagination.” The cleaning and rehabilitation of the river would create a lasting legacy, including enabling swimming again in its waters, officials said. The marathon swimming event and the swimming leg of the triathlon are the two sporting events scheduled to take place in the Seine. The opening ceremony, scheduled for July 26, will also include a parade of athletes on the Seine with boats for each national delegation. 

Swimming in the Seine was officially banned in 1923 due to pollution and danger from passing river barges. When Paris hosted the 1900 Olympics, swimming events were held in the Seine. In 1990, Former French President and then the Mayor of France Jacques Chirac promised to make the Seine clean enough to swim in it, but couldn’t achieve their target.  

Cleaning the Seine

Escherichia coli and Enterococci, two bacteria commonly found in faecal matter, have plagued the waters of Seine for decades. Conducting quality checks in the Seine involves monitoring levels of these two microbes in the water through daily samples at four points — Bercy (right bank), Marie’s Arm, Pont Alexandre-III – Olympic site, and Grenelle Arms.

A 2006 European directive that lays the guidelines to monitor the quality of bathing water is used to regulate the water quality in the Seine. Bacteria concentration in the river increases when wastewater is discharged into the river during heavy rainfall.

The Parisian sewage system, which has been called the “flagship of France’s industrial heritage” by a museum in Paris dedicated to the history of sewers, acknowledges its role in the hygienic sanitation of the capital city.  

In the past, the city’s sewers have been the reason for the extensive spread of disease as was seen at the end of the 18th century.  

Georges-Eugène Haussmann, who served as the prefect of Seine from 1853 to 1870 under Napoleon III, carried out extensive public works which included improving the old sewage system in the city.  

Paris has a combined sewer system, which means that the wastewater and stormwater flow through same pipes. Heavy rainfall overwhelms this system, and raw wastewater is discharged into the Seine instead of treatment plants.  

“The Seine is not a special case,” Metin Duran, a professor of civil and environmental engineering at Villanova University who has researched stormwater management, explained to the Associated Press. “It really is a complicated and very costly problem.”

An important part of the Seine cleanup process is the Austerlitz basin, a 50,000 cubic metre basin (equivalent to 20 Olympic swimming pools) that will store wastewater and stormwater during heavy rainfall. This excess water will then gradually flow into the sewer network to be treated in a treatment plant. The Austerlitz basin was inaugurated in May.

To call the Seine one of the most romanticised rivers would not be an understatement. In her book The Seine: The River that Made Paris, author and New York Times journalist Elaine Sciolino compares its (or rather, her, as Ms. Sciolino says) “romantic power” to its “human scale.”

“Compared with the Nile, the Amazon, or even the Hudson, she feels accessible, narrow enough to track the comings and goings on either side. Her banks are flat, her bridges densely packed and so low to the ground that you can almost touch the water,” she writes in her book, essentially an ode to the river.  

But even extensive romanticisation has not saved the Seine from being polluted over centuries. Apart from the two microbes that Seine’s swimmability depends on, many other physical and chemical pollutants added to the river over the years have led to its current murky image.

Joint research conducted in February 2024 by the European Pesticide Action Network (PAN Europe) and its members revealed an increase in the contamination of European fruit and vegetables with pesticides from the per- and polyfluoroalkyl substances (PFAS), also known as “forever chemicals.” The report focused on its terminal degradation product trifluoroacetic acid (TFA) which is highly persistent. TFA was present in all tested water samples, including the Seine. Out of 23 tested European surface water samples, the Seine had the second-highest concentration of TFA.

Authorities had, in 2015, started working on making the Seine swimmable for the 2024 Paris Olympics and beyond. Apart from the Austerlitz storage basin, two disinfection units of the SIAAP (Paris Public Sanitation Service) treatment plants became operational in summer of 2023.

According to officials, the water quality of the Seine is scheduled to be tested twice daily during the Games. Both triathlon and marathon swimming have contingency days scheduled within the calendar, and any decision to postpone an event would be taken by the Paris 2024 teams together with the International Federation and in coordination with the International Olympic Committee, in the early morning on the day of the scheduled competition.

“We have great confidence in the work of the City of Paris and the relevant State authorities to ensure the water quality will meet the necessary standard,” a Paris 2024 spokesperson said.

After the 2024 Olympics, Paris city authorities are hopeful of opening three bathing sites in the Seine in 2025: Bras Marie (Parc des Rives de Seine, on the right bank), Bras de Grenelle, and Bercy.