Paris has poured a staggering 1.4 billion euros into cleaning up the Seine River, hoping to transform it from a polluted waterway into a venue fit for Olympic athletes. Yet, even with this massive investment, the river’s high levels of bacteria remain a concern, raising questions about whether the city’s ambitious efforts will be enough to make the Seine swimmable once again.
Despite massive efforts to improve water quality for the Olympics, Paris still grapples with pollution challenges in the iconic Seine River
Paris has invested a staggering 1.4 billion euros (about 10.5 billion yuan) to improve the water quality of the Seine River, but concerns remain over its cleanliness, particularly its high levels of bacteria. This raises questions about the effectiveness of such a significant investment.
In recent years, the water treatment industry has been at the forefront of technological innovation, driven by the increasing demand for environmental protection and sustainable development. With the global spotlight on water quality, events like Watertech China in Shanghai showcase the latest advancements in water treatment, from ultrapure water technologies to wastewater management solutions. Despite these innovations, even cities like Paris, with massive resources at their disposal, still struggle with water quality challenges.
On July 31, during the 33rd Summer Olympics, 55 female athletes plunged into the Seine from a platform under the Alexander III Bridge to kick off the triathlon competition. Two hours and 45 minutes later, 55 male athletes followed. The excitement of the athletes was matched by the Paris municipal government, which had spent years and a substantial amount of money to make this event possible in the iconic river.
Back in 2017, when Paris won the bid to host the Olympics, the city made a bold promise: to hold part of the competition in the Seine. This commitment was met with surprise across France, as the Seine had been notorious for its pollution. Swimming in the river had been banned since 1923 due to severe water contamination, and the ban has never been officially lifted.
The challenge of improving the Seine’s water quality became even more apparent as the Olympics approached. The men’s triathlon, initially scheduled for July 30, had to be postponed due to poor water quality. The culprit? Excessive levels of E. coli and enterococci—bacteria commonly associated with fecal contamination.
So, why is this romantic river, which flows through the heart of Paris, so polluted? The answer lies in the city’s antiquated drainage system, which dates back to the mid-19th century.
Paris, like many major cities of that era, uses a “combined sewer system,” where domestic sewage and rainwater are channeled through the same pipes. In simple terms, wastewater from homes mixes with rainwater in underground pipes and is then treated at sewage plants. However, during heavy rainfall, the volume of water can overwhelm the sewage treatment plants, causing the mixed sewage to overflow.
To prevent this overflow from backing up into homes, engineers designed the system to divert excess sewage directly into the Seine during storms. This means that whenever there is significant rainfall, a mix of sewage—including fecal matter—is released into the river. According to Paris officials, this kind of discharge occurred around 12 times a year before the Olympics, explaining the persistent high levels of “poop content” in the Seine.
Despite the city’s extensive efforts and investment to clean the river, the challenge of managing its historic drainage system remains a significant hurdle. As Paris continues to grapple with this issue, it underscores the complexities of urban water management, even in one of the world’s most iconic cities.
In addition to its combined sewer system, many ancient towns around Paris have sewage pipes from residential homes that lead directly into the Seine and its tributary, the Marne River. Adding to the pollution are about 170 houseboats moored along the Paris section of the Seine, where wastewater from onboard residents is also dumped straight into the river.
To tackle the high “poop content” in the Seine, the Paris government has launched an ambitious series of engineering projects. One of the most significant undertakings is the construction of a massive underground water storage tank near the Austerlitz train station. This tank, capable of holding 46,000 cubic meters of water—about the size of 20 Olympic swimming pools—is designed to capture sewage during heavy rainfall. Instead of the sewage being discharged into the Seine, it is redirected to this reservoir, where it is held until the rain subsides and can be gradually released into the sewage treatment system.
However, this solution has its limitations. The Austerlitz reservoir project aims to reduce the number of sewage overflows into the Seine from 12 times a year to just 2. But if Paris experiences prolonged or intense rainfall during the Olympics, the reservoir could exceed its capacity, and untreated sewage, including fecal matter, could still end up in the river.
Addressing the problem of direct sewage discharge from residential homes, Paris has initiated a door-to-door campaign to encourage residents to connect their sewage systems to the municipal pipeline. They’ve also installed new sewage pipes and pumps at docks where houseboats are moored, offering subsidies of 6,000 euros per household (or boat) to those who cooperate with the upgrades.
Despite the 1.4 billion euros invested, the coordination of multiple departments, and the controversies that have arisen, the effectiveness of Paris’ water management efforts ultimately depends on the levels of E. coli and enterococci in the river. According to the World Swimming Federation’s Open Water Swimming Manual, these bacteria are reliable indicators of fecal contamination.
For the triathlon to proceed safely, the water quality of the Seine must meet strict standards: E. coli levels must not exceed 1,000 colony-forming units per 100 ml, and enterococci levels must remain below 400 colony-forming units per 100 ml. Failure to meet these standards could result in athletes suffering from diarrhea, vomiting, and respiratory infections.
To ensure compliance, water samples must be taken at three points along the competition course—2 months, 7 days, 48 hours, and on the day of the event—with the worst result used as the final water quality standard.
Due to continuous rain on July 26 and 27, the water quality test on July 30 failed to meet the standard, forcing the Paris Olympic Organizing Committee to postpone the men’s triathlon by a day. Fortunately, by July 31, the water quality had improved, allowing both the women’s triathlon and the rescheduled men’s event to proceed without further issues.
The Paris Olympic Committee likely breathed a collective sigh of relief—1.4 billion euros well spent! Even better, France hopes to sustain these water quality improvements beyond the Olympics. The mayor of Paris has announced plans to open several public swimming points along the Seine by 2025. This would allow both locals and tourists to not only enjoy the river from its banks but also experience the “romantic river” firsthand, finally diving into its waters 101 years after swimming was banned.