Is Paris’s Stormwater Management the Real Olympic Challenge?  

9 Jul 2024  |  Chloé Meyer

On 26 July, the city of Paris will open the Olympic and Paralympic Games, and water will be front and center. The Seine River, which flows 13 kilometers through the city from east to west, plays a significant role in this year’s Games: In the opening ceremony, cruise boats will carry athletes and delegations past an anticipated 300,000 spectators, and three competitions will take place in the river (the Olympic and Paralympic triathlons and the Olympic marathon swimming race).

One big question remains: Will the Seine be clean enough to allow athletes to swim in it? Incidentally, this isn’t the first time that the Olympics has raised water-related questions, and it’s worth a deeper look.

Water quality in the Seine is a century-old issue: In 1923, authorities forbade swimming in the river because of pollution and traffic. The dream of making the Seine swimmable is not new: In 1988, Jacques Chirac, then mayor of Paris (and later president of the country) and running for reelection, promised to improve the river quality and take a bath in it. That never happened. At the end of the 2000s, a derogation was granted to allow triathletes to swim in the river, but it was withdrawn in 2013 because of the high levels of bacterial contamination leading to gastroenteritis, urinary tract infections, meningitis, and septicemia. 

While French President Emmanuel Macron and Paris Mayor Anne Hidalgo announced they would bathe in the river before this year’s Games, they have yet to take a dip, as the quality of the river has remained below expected levels. French swimmers skipped training in June because of high levels of E. Coli (up to eight times the maximum limit set by World Aquatics). On June 26, the regional prefect warned that the Seine was still not expected to meet required bathing quality standards at the beginning of July because of the ongoing consequences of the rainfall events that took place over the last few weeks. 

France has been preparing for the Games by investing in infrastructure upgrades to improve water quality:
 A few months after Paris was awarded the Games in September 2017, the French state, together with the city of Paris, launched a ‘plan baignade’ (i.e., ‘bathing plan’). The plan features a €1.4 billion (US$ 1.5 billion) investment package designed to ensure that the Seine reaches the required bathing quality for relevant competitions and that efforts last beyond the Games, with the implementation of bathing facilities in Paris and other surrounding municipalities starting in 2025. 

The bathing plan specifically aims to reduce bacterial pollution by 75%, as the presence of E. coli and Enterococcusindicates contamination with raw sewage. Consequently, two of the upstream wastewater treatment plants have been retrofitted with disinfection units that are supposed to improve water quality by two-thirds in dry weather. Harbors upstream of Paris have also been equipped with sanitation networks and stormwater capture systems for €12.5 million (US$13.4 million). Actions to reduce permanent pollution are also underway, aiming to fix around 23,000 incorrect wastewater network connections discharging raw sewage in the river, for an expected cost of €300 million (US$322 million). 

Stormwater management is front and center, with the implementation of grey infrastructure (gutters, pipes, and underground basins): From its 19th century transformation, Paris inherited a combined sewer network that collects both stormwater and wastewater. In wet weather, the network is easily saturated, leading to the discharge of untreated sewage through combined sewer overflows (CSOs). The bathing plan’s efforts have heavily focused on improving stormwater management, with the construction of dedicated treatment stations and improvements of processes to eliminate CSOs during normal rainfall events. The plan aims to limit the use of the 44 Parisian CSO outfalls to extreme rainfall events, leveraging the new infrastructure to allow the Seine’s water quality to bounce back within 48 hours of a rainfall event. 

Efforts culminated in the commissioning of Paris’s new giant detention basin—the Austerlitz basin—in May 2024, after three-and-a-half years of construction. Described as an underground cathedral, the €90 million (US$96 million) basin measures 30 meters in height and 50 meters in diameter; it can hold up to 50,000 m³ (20 Olympic swimming pools) of raw storm- and wastewater to prevent their discharge into the river, releasing it slowly into the sewer network for treatment once the rainfall event subsides. Additional stormwater infrastructure upstream of Paris is slated for completion in the coming weeks and months, including stormwater treatment stations and additional basins and tanks. 

Still, short-term fixes to long-term water management challenges are failing to sustainably address systemic challenges. The reliance on expensive, artificial, and maintenance-intensive grey infrastructure solutions to make the Seine swimmable for the Games illustrates the difficulty in changing water resource management practices when pursuing short-term objectives. It also fails to align with the approach advocated by the city’s ‘Paris Plan Pluie’ (i.e., Paris Stormwater Plan), a zoning program launched in 2006 that pursues stormwater infiltration at the hyperlocal scale. 

At the time of the announcement of the bathing plan, less than 40% of the Seine River basin had reached ‘good’ ecological status—a quality-level achievement required by the EU Water Framework Directive by 2015. Improving the quality of the river was not a priority then—given the high costs of preventing and eradicating pollution stemming from both agriculture and urbanization practices—for solely environmental benefits. Sustainably managing local and diffuse pollution sources requires strengthened coherence between public policies covering water, urban planning, agriculture, and other sectors. The timeline for improving the global quality of river basins is significantly longer than that of political mandates and event organization calendars. 

Sustainably managing local and diffuse pollution sources requires strengthened coherence between public policies covering water, urban planning, agriculture, and other sectors.

In the face of these unrealistic expectations, Olympian swimmers are left to hope for no rain, as the time has run out to structurally improve the quality of the Seine for the competition. This is yet another example of the need to preemptively invest in water resources management so we can avoid short-term fixes at the expense of athletes, citizens, and the environment.