Paris Olympic Athletes Face Concerns Over Seine Water Quality

The Olympics are known for surprises. For marathon swimmers and triathletes, one of those surprises could be the venue, which is often an ocean, lake or, in the case of the Paris Olympics, the city’s historic Seine River.

While the Seine is iconic, offering picturesque views of landmarks like the Eiffel Tower and the Musee d’Orsay, it’s also a contaminated body of water. The city has banned swimming in the Seine for over a century due to health risks.

But Olympic organizers sought to change that, even temporarily, by hosting the marathon swimming and swimming portion of the triathlon in the river. They invested $1.5 billion to build a large tank beneath the Seine to collect stormwater during heavy rains and storms. The water in the tank is then gradually channeled to a wastewater treatment facility, where it’s treated, and the clean water is returned to the Seine. Engineers also upgraded sewage pipes from boats and docks along the Seine to minimize the amount of contaminated sewage entering the river.

However, as of the end of July, testing continues to show unsafe levels of bacteria, particularly E. coli and enterococcus, in the water. The levels fluctuate based on various factors, including rainfall, sunshine, and river current speed. According to weekly reports released by Paris officials, the river met European swimming standards for six out of nine days between June 24 and July 2.

Still, in an effort to demonstrate their confidence in the Seine’s cleanliness and safety, Paris 2024 organizing committee president Tony Estanguet, took a dip in the river on July 17, even submerging their head for some freestyle strokes. “After the Games we will have a swimming pool in the river for all the people,” Hidalgo after her dip.

Whether that happens remains uncertain. The final decision on whether to hold the marathon swimming and swimming portion of the triathlon in the river will be made by the respective sports’ governing bodies, based on data gathered by Paris officials from the day before and morning of the scheduled events. According to , a meeting with stakeholders—Paris officials, Paris 2024 Olympic authorities, the sport’s federation, regional authorities, and Meteo France (the country’s meteorological organizations)—will occur at 3:30 a.m. Paris time on each event day to make a final decision on whether the athletes will compete in the Seine.

That assumes, of course, that E.coli lab testing can be completed quickly enough to provide reliable measurements, says Natalie Exum, assistant professor of environmental health and engineering at Johns Hopkins Bloomberg School of Public Health. “It takes about 24 hours to culture E. coli bacteria,” she says. “There may be some other proxy indicator for bacteria that they are using, but it’s not like you can stick something in the water and know how many E. coli are present in that instant.”

If the river continues to have fluctuating levels of pollutants, athletes could face health risks if officials declare the river safe for swimming during the scheduled event. The most common organic contaminants—E. coli and enterococcus bacteria—are responsible for gastrointestinal illnesses, including diarrhea, abdominal cramps, vomiting, and nausea—not something anyone welcomes, especially athletes needing peak physical condition for competition. “There are certain pathogenic strains of E. coli that cause what we call traveler’s diarrhea,” says Dr. Susan Kline, professor of medicine at the University of Minnesota Medical School. Kline says anyone exposed to untreated water might expect risks similar to those that campers might face in rivers or lakes, including parasites like giardia.

Then there are potential chemical pollutants from industrial waste runoff, which could pose serious health risks, as well as skin irritation. Additionally, having cuts or open wounds on the skin could increase the risk of infection from whatever is in the water, says Dr. Timothy Brewer, professor of medicine at epidemiology at University of California Los Angeles.

It’s not as if the sewage system in Paris and the river are intentionally connected. During heavy rain, the sewage flowing into water treatment plants gets mixed with rainwater overflow, and the facilities’ normal treatment systems become overwhelmed by the sheer volume of water requiring treatment. Some of that untreated water then flows into the Seine, contaminating the river. “We call that first flush,” says Exum of the flood of water that gushes through wastewater treatment plants after rainfall. “I would not advise anybody anywhere in the world to swim in a river 24 hours after a major flush,” she says. “The whole sewer system is designed to manage the low flow capacity of toilets, not gushing water. These systems are not designed for the intensity of rain events that we are now seeing as a result of climate change.”

Even with heavy rain, typically, some sewage-derived bacteria could be killed off by ultraviolet sunlight and higher temperatures. However, a rainy and cloudy spring in Paris has created ideal conditions for bacteria to thrive in the river. The forecast for the first week of the Games is cloudy. Even with the overflow tank officials built to catch sewage during downpours, the river continues to host unsafe levels of bacteria.

The tank is an essential but insufficient step to truly cleaning the Seine, says Exum. “To decouple the rainwater system from the sewer system all throughout Paris is what essentially needs to happen but that takes decades, and is an iterative process.” Cities like Paris with limited green spaces to absorb rainwater end up sending most of it into the sewer system underground, which just increases pollution in the river.

Organizers that the Seine’s water will be tested twice daily as the Games approach, and that an alternative venue for marathon swimming is available at Vaires-sur-Marne. They also have a contingency plan to delay the triathlon or remove the swimming portion entirely if the river is deemed unsafe on competition days. But no official announcement has been made, and for now, the two Seine events are scheduled for the city’s river.

The uncertainty adds to the already stressful situation for athletes, who would appreciate a decision on where, and if, they will be competing, and reassurance of their safety during competition. Team USA open water coach Ron Aitken that the lack of a decision is “irresponsible.”

“I think that even if there is a 1% chance that the race isn’t going to be held because of cleanliness or lack of cleanliness, you need to have a backup plan,” Aitken said. “It’s the Olympics.”