Key TakeawaysParis invested $1.5 billion in wastewater management projects to clean up the Seine, but fecal bacteria could still make the river unswimmable.Recent testing shows water quality in the Seine can still fail to meet the safety threshold on some days.Fecal bacteria levels in beaches and rivers might peak in the 48 hours after heavy rain.

Key Takeaways

Paris invested $1.5 billion in wastewater management projects to clean up the Seine, but fecal bacteria could still make the river unswimmable.Recent testing shows water quality in the Seine can still fail to meet the safety threshold on some days.Fecal bacteria levels in beaches and rivers might peak in the 48 hours after heavy rain.

The city spent around $1.5 billion on wastewater management projects to clean up the Seine, but high bacteria levels could still delay or cancel Olympic swimming events in the river.

However, these numbers can change “daily and hourly,” especially if it rains, saidKartik Cherabuddi, MD, FACP, an infectious disease specialist and professor in the Division of Infectious Diseases and Global Medicine at the University of Florida College of Medicine.

“This is especially important with Paris and the Seine, where overflow from old sewers can cause contamination. We know that a rainy day tends to be worse,” Cherabuddi told Verywell.

Swallowing contaminated river water can cause diarrhea, stomach cramps, rashes, eye infections, or ear infections.

“Even though [the athletes] are professionals and extremely healthy individuals, if you give even a healthy volunteer a higher amount of infectious dose, it can make them sick,” Cherabuddi said.

Surfrider Foundation Europe, a nonprofit organization focused on beach preservation and water quality, has also monitored the Seine for E. coli and enterococci bacteria every two weeks since September 2023.

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Heavy Rainfall Could Lead to Sewer Overflow

To make the Seine swimmable, Paris spent three years building a massive retention tank to keep untreated wastewater from flowing into the river after heavy rain. This tank, known as theAusterlitz basin, was ready for use at the end of May.

“This retention tank will hold the wastewater that would have otherwise gone into the Seine untreated, and then it will slowly flow into the wastewater treatment plant. That’s not taking care of everything. It will certainly have an impact, but my greatest concern is that there hasn’t been enough time to test its effectiveness,”Natalie Exum, PhD, an assistant professor of environmental health and engineering at the Johns Hopkins Bloomberg School of Public Health, told Verywell.

Exum said that even with the new retention tank, Paris’s old sewage systems may leak, allowing pathogens to leach into the ground and travel to the river after a heavy rain event.

“The riskiest time to go swimming at a beach or in a river is the 48 hours after any heavy rain event. That’s when then washout of fecal bacteria is greatest, increasing your risk of gastrointestinal illness,” Exum said.

Last year, heavy rain led to unsafe bacteria levels in the Seine, forcingWorld Aquaticsto cancel an open water swimming event. Olympic officials will continue to monitor the Seine to make a decision about the upcoming marathon, triathlon, and paratriathlon events.

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Should You Swim in an Urban River?

“The usual answer is no, things tend to just fall off when there’s not as much scrutiny,” Cherabuddi said.

Paris isn’t the only city trying to clean up its urban river.Berlinhas made efforts to open its river to swimmers, and the London mayor recentlyannounced plansto make the city’s rivers swimmable within 10 years. Copenhagen cleaned up its harbors decades ago, and swimmers canreview water quality onlinebefore going for a dip in Denmark’s capital city.

Even if the athletes can complete in the Seine this summer, you should consider your own health risks before diving into the river next year.

“The risk factors of the general public tend to be very different from these elite athletes who are probably the fittest in the world,” Cherabuddi said.

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What This Means For You

1 SourceVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Environmental Protection Agency.What affects human health at the beach.

1 Source

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Environmental Protection Agency.What affects human health at the beach.

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

Environmental Protection Agency.What affects human health at the beach.

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