Rain fell on athletes, spectators, can-can dancers, and opera singers at the 2024 Paris Olympics opening ceremony on July 26th. More rain over the weekend reportedly led to an increase in disease-causing bacteria in the Seine River, prompting officials to cancel a triathlon training session and postpone the men’s race. Finally, on Wednesday (July 31), both the women’s and men’s triathlons were allowed to proceed with athletes swimming in the Seine before cycling and running. France and Great Britain won gold in the women’s and men’s races, respectively. However, concerns remain about the water quality in the Seine, with the mixed relay and marathon swimming events scheduled for next week.
Paris invested heavily in making the Seine swimmable for the Olympics, including connecting thousands of residences to municipal sewer systems and constructing a massive underground cistern. This cistern, holding the equivalent of 20 Olympic swimming pools of water, aims to prevent untreated sewage from entering the river. Paris has a combined sewer network that captures stormwater and wastewater, but during heavy rain, untreated water is diverted into the Seine to prevent backups. The new cistern helps by capturing excess water and slowly releasing it back into the sewers for treatment.
Despite these efforts, heavy rainfall still leads to a spike in bacteria in the Seine, particularly Escherichia coli (E. coli). E. coli is a bacterium found in human and animal feces and acts as an indicator of fecal contamination. Its presence suggests that other poop-borne pathogens, such as norovirus and Salmonella, are also likely present.
Following a rainstorm, E. coli levels typically decrease due to sun exposure and fluctuating water temperatures, taking days, not weeks. However, factors like upstream runoff, land use, and drainage systems can affect the rate at which these levels drop.
A rainstorm hit Paris in the early morning hours of Wednesday, July 31st. Organizers met to discuss the latest water-quality tests, which deemed the water safe for racing. While the tests were conducted 21.5 hours before the races, the results of tests taken on Wednesday have yet to be released.
World Triathlon, the international governing body for triathlons, bases its water safety guidelines on the European Union’s Bathing Waters Directive. These guidelines set a threshold for safe E. coli levels in inland waters at 900 colony-forming units per 100 milliliters (CFU/100mL). This threshold is based on epidemiological studies correlating swimmer illness rates with E. coli levels in the water.
Paris Mayor Anne Hidalgo and Paris 2024 Chief Tony Estanguet took a dip in the Seine two weeks before the Games to demonstrate its cleanliness. However, data revealed that E. coli levels were 985 CFU/100mL that day, slightly above the safe threshold.
Swimming in poop-contaminated water poses various risks, including stomach cramps, diarrhea, dehydration, and ear, eye, respiratory, and wound infections. While most E. coli strains are harmless, some can cause gastrointestinal problems, urinary tract infections, and in severe cases, bloody diarrhea, blood clots, and kidney damage.
The risk of getting sick after swimming in contaminated water depends on individual immunity and exposure to germs. Swallowing contaminated water poses the greatest risk, but skin exposure can also be a concern. Swimmers can protect themselves by wearing earplugs, nose plugs, and goggles; covering open wounds with waterproof bandages; changing bandages after swimming; and showering after swimming.
With more rain expected in the coming days, the water quality of the Seine may continue to fluctuate. The upcoming races could be postponed, modified to exclude swimming, or moved to alternate venues. Only time will tell if the water quality remains safe for athletes and spectators alike.
