Envisaging the Seine as an Olympic basin was like diving into the water without really knowing how to swim. Nearly ten years ago, when the City of Paris determined its “action plan” to bid for the Olympic and Paralympic Games, planning to host marathon swimming, triathlon, and para-triathlon events in the Parisian river had been met with raised eyebrows due to its reputation. “It’s true that we are completely changing our approach to a river that has been neglected from an environmental and bacteriological point of view for a century,” says a stakeholder in the project.
The Seine had been off-limits for swimming since a decree dating back to 1923 due to high concentrations of escherichia coli and enterococci, fecal bacteria from sewage discharged into the river during rainy weather to prevent sewer overflow in the city. 1.4 billion euros were allocated to modernize the sewage network and make the Seine cleaner. The key weapon, along with other large-scale projects launched around the capital, is a massive retention basin located at Austerlitz.
The Austerlitz basin, the ultimate weapon
“We needed an element that Paris did not yet have within the city limits to prevent sewage discharges between the bridge and the future bathing site, that is, between Bercy and the Eiffel Tower,” explains Samuel Colin-Canivez, responsible for major sewage works in Paris. The idea is simple to understand: it is a storage structure that allows sewage to be held back until the rain passes. Once the rain has stopped, the sewage network is no longer overloaded, and the basin can be emptied back into the network by pumping it. Instead of being discharged into the Seine, the water will follow its usual path to be treated at a sewage treatment plant.
In total, 44 months of work and over 90 million euros were needed to build this immense basin with a storage capacity of around 50,000m³, equivalent to about twenty Olympic pools. It is partly this basin that underpins the goal of maintaining the triathlon (July 30, 31 and August 5), marathon swimming (August 8 and 9), and para-triathlon (September 1 and 2) events at the 2024 Paris Olympics.
Last summer, several test events in the Seine ended in disaster. The Open Water Swimming World Cup leg was canceled due to high water pollution levels after heavy rainfall. The para-triathlon and mixed relay swimming events were also canceled, this time not due to weather issues. However, the City of Paris cited a “malfunction of a valve” in the sewage system to explain the water quality deterioration.
The men’s and women’s triathlons were still held. Despite the bacteriological thresholds not guaranteeing good water quality and were in fact unknown for the men’s event due to lab analysis issues. The swimming and triathlon federations set the escherichia coli bacteria concentration threshold at 1000 CFU (colony-forming units) per 100 ml. However, this is the limit not to exceed. They consider the barrier between good quality water and acceptable quality water to be 500 CFU/100 ml. We will never reach zero risk as there can be rainfall that occurs only once every 100 years.
In a report from the Regional Health Agency on July 23, 2023, it is reminded that the European Parliament sets the limit at 900 CFU/100 ml. An analysis by FranceInfo showed that the water quality in the Seine in summer 2023 was far from satisfactory.
Asked about this, the City of Paris seeks to reassure. The lab manipulation issues? “We have implemented a dual process,” assures Pierre Rabadan, deputy in charge of Sports, Olympic, and Paralympic Games. “The samples will be sent to two different laboratories and handled by different personnel. In case of mishandling by one team, they can be replaced by the second team, which will also confirm the analysis to ensure they are provided on time.”
The defective valves? “This is part of the resilience plan we have put in place,” reassures the former rugby player. “The maintenance teams will have much closer monitoring of the underground network, including human monitoring, to be able to detect a potential malfunction in real-time by going directly into the sewers. It allows for visual control and the potential malfunction to be resolved almost immediately.”
One uncontrollable factor remains: rain, which disrupted the marathon swimming events last summer. “We hadn’t seen such rainfall in an equivalent period since 1965,” recalls Anne Hidalgo’s deputy. “The whole point of the plan and the work that has been done is to delay the need to discharge water into the Seine during the two heaviest rainfall periods,” explains Samuel Colin-Canivez, responsible for major sewage works in Paris. “To delay this need to the heaviest rainfall of the year would require enormous investment efforts, simply for a few additional days of swimability. It wouldn’t be worth it, knowing that we will never reach zero risk as there can be rainfall that occurs only once every 100 or 1000 years.”
Athletes will swim in the Seine… or they won’t
The stakeholders in this plan refuse to consider the unthinkable. “The event we experienced last year is so rare that it would be even rarer to experience it two years in a row,” insists Pierre Rabadan. “I’m not a statistics expert, but it seems more likely to me that we would host the Games a second time within the next 20 years. The Austerlitz basin and other upstream structures in Paris allow us to be resolutely optimistic in a scenario that is not that of a devastating hurricane bringing 15 days of rain.”
That’s why for months, the organizers have refused to discuss a plan B. At the Olympics, athletes will swim in the Seine. Or they won’t. To further reduce the risk, the organizing committee and federations are working on contingency days that would allow events to be postponed if water quality does not meet swimability criteria.
Among the athletes, this determination to keep the events in the Parisian river – which also meets cost and organizational requirements – is divisive. “It’s a concern,” says Brazilian Ana Marcela Cunha, the reigning Olympic champion in open water swimming, in an interview with AFP. “There was no test event last year, but the organizers insist on having the events there. […] A plan B is needed in case swimming is not possible.”
“I think the COJO (organizing committee) is really putting pressure on itself to ensure everything goes as planned,” says Dorian Coninx, the reigning world triathlon champion and a strong French medal contender. “The opposite would be a disaster for them.” For this specific discipline, the last resort might be to remove the swimming event and only have the cycling and running. “It would be problematic if it turns into a duathlon,” says the Frenchman. “We train hard to do triathlon, and it would bother everyone, including the medalists, to be on the podium of a triathlon that ultimately isn’t one.”
For these elite athletes, the sporting stakes outweigh everything else.
