How Paris Cleaned Up The Seine & Created A Better City For Its Citizens
The Seine is an iconic river. With a length of 481 miles, it runs from Burgundy through Paris out to the sea in Normandy. For all its fame, the Seine has a much darker side — it has been a dumping ground for all kinds of waste. Its biggest source of pollution in contemporary times has been the disposal of countless tons of wastewater—which include domestic and industrial sewage—into the river.
The estimated cost of the recent Seine cleanup efforts amounts to 1.4 billion euros ($1.5 billion), paid by the state and local authorities. More than half a billion euros was designated for huge storage basins and other public works that reduced the need to spill bacteria-laden wastewater into the Seine, untreated when it rains.
The 2024 Olympic deadline supercharged a Seine cleanup that had been decades in the making, infusing social, environmental, and economic benefits for Paris and the surrounding communities in the process.
The Seine is key to French life, culture, and identity, and the river and its banks were the centerpieces of the Paris 2024 Olympic opening ceremony. As the Seine narrows and cuts through the heart of Paris, it carries centuries of history with it. Tourists in town for the Olympics meandered along the Seine’s banks, and their paths mirrored the premier architects who constructed the Eiffel Tower, the Notre Dame Cathedral, and the Louvre and Orsay museums.
How did the Seine Become So Polluted?
For centuries, the Seine had been a dumping ground for laundry suds, human waste, and animal parts tossed by medieval butchers. In the 19th century, factory and human wastewater was often discharged directly into the Seine.
City planner Baron Haussmann’s decisive urban renewal project throughout the second half of the 19th century was an engineering triumph for Paris, as National Geographic relates, yet it was dangerous for the Seine’s health. Such waste disposal directly into the Seine seemed the only option to avoid saturating Paris’ sewage network and flooding the city when especially heavy rain hit. Seine swimming was banned starting in 1923, the year before Paris last hosted the Olympics, due to the health risk posed by a river contaminated by the city’s wastewater.
In 2015, Paris launched its plan “baignade,” or swimming plan, with detailed measures to clean the Seine and Marne, a tributary, and make the Seine swimmable by the 2024 Olympics—an essential element of its successful bid to host the games. The plan was necessary because the city needed to eradicate the E. coli, enterococci, and other assorted micro-organisms that for centuries had sickened swimmers. Bloomberg comments that “the cleaning of the Seine helps to burnish Paris’s brand as a new capital of sustainability.”
To achieve this accolade, however, Paris had to connect more than 23,000 residences, as well as houseboats, to the municipal sewer systems, which previously had dumped untreated wastewater into the rivers.
City officials told Time magazine, that, as a result of recent infrastructure upgrades, the amount of untreated wastewater that ended up in the Seine in 2022 was 90% lower than 20 years earlier. Despite this progress, though, pollution was still a problem. In 2022, 1.9 million cubic meters of untreated wastewater had spewed into the Seine. More work remained to be done.
The Infrastructure that Cleaned Up the Seine
To clean up the river fully, several new structures had to be built.
Wastewater and rainwater had flowed into the same drainage pipes. To remedy this, Paris built a 15 million gallon underground tank to store water — the Austerlitz rainwater retention basin was completed in May 2024 and has a holding capacity of around 50,000 m3. This giant reservoir dug next to Paris’ Austerlitz train station aims to collect excess rainwater and prevent bacteria-laden wastewater from entering the Seine. It can hold the equivalent of 20 Olympic swimming pools of dirty water that will now be treated rather than being funneled raw through storm drains into the river.
Exceptional weather events will be easier to deal with thanks to the new basin, as it will prevent wastewater from being discharged into the Seine during heavy rainfalls. Excess water will flow into the sewer system and be treated. The new storage basin “guarantees” that water can be stored even during severe storms and will help water levels to “return to normal as quickly as possible,” said Paris mayor Anne Hildago, as reported by AP.
An overhaul of sewage processing across the region now ensures that clean water moves into Paris. Financial incentives and a publicity campaign encouraged rural households and houseboat owners upstream of Paris to stop discharging toilet waste directly into the river, diverting it instead into the sewer system. In total, upstream of Paris some 23,000 connections have been or are being being treated.
To stop wastewater discharges from boats or floating buildings docked in Paris ports along the Seine, the law now requires each boat or structure to be connected to the main wastewater networks of the the city.
The biggest sewer project was an 8.8 kilometer (5.7 mile) super-sewer built south of the city. Two disinfection units at the SIAAP (Service public de l’assainissement francilien) wastewater treatment plants, on which much of the improvement in water quality depends, have been operational since last summer.
Wired describes how there will be more public investments in improving the public water treatment system, and authorities will also be working with the private sector to ensure existing and new homes and buildings meet the right standards. In the coming years, the prefecture will continue rationalizing the sewer and water treatment system, making sure that buildings are properly connected to the network and not to the river directly, and that the network has sufficient capacity to avoid being overwhelmed.
What Environmental Effects has the Seine Cleanup Had?
About 35 fish species are now living in the Paris section of the river, up from only three in the 1970s, when waters were extremely polluted due to nearby industrial activities. The revival of fish stocks has been accentuated by the restoration of river foliage.
A clean Seine also offers Parisians an escape from steamy summer temperatures. After the games, the river should reopen to everyone — in the summer of 2025. representatives from City Hall say a handful of bathing spots are within Paris itself, with others a bit further away from the city center.
- Bras Marie (Parc des Rives de Seine, right bank), with organized water sports events;
- Paris Plages, where swimming during the Olympics was permitted;
- Bras de Grenelle, between the Port de Grenelle and the banks of the Ile aux Cygnes (15th district); and,
- Bercy, at the Passerelle Simone de Beauvoir, below the Parc de Bercy (12th arrondissement)
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