The Seine River's Contamination: Assessing the Risks for Olympic Athletes

Paris’ iconic River Seine continues to be the backdrop for Olympic controversy due to poor water quality and contamination concerns.

On Tuesday, Olympic organizers postponed the men’s individual triathlon race—which was scheduled to take place later that day—after water tests of the Seine showed the river to be unsafe for athletes, primarily due to the presence of Escherichia coli (E. coli).

That event and the women’s triathlon are both now scheduled to take place on Wednesday, pending additional tests on water quality levels.

Water contamination isn’t new to the Seine—it’s been illegal to swim in the Parisian river for more than a century due to pollution concerns. The river was given the OK to swim in by Olympic organizers after a nine-year and $1.5 billion investment to clean it up—the city’s mayor even took a dip in mid-July to demonstrate its new cleanliness.

Though the Seine was officially cleared for swimming through testing in the days leading up to the Olympic Games, heavy rainfall has complicated matters. According to NPR, the city’s antiquated water system has been overwhelmed by the unusually wet weather, forcing untreated sewage into the river.

As the world waits to see if these triathlon events make it to the Seine—or if they instead become duathlons—here’s what you need to know about water contamination and how it can affect the human body.

World Triathlon, the governing body for triathletes, has only stated that the water quality in the Seine does not comply with the established thresholds set by the organization for swimming.

However, multiple news outlets have reported that the concern is over higher-than-acceptable levels of E. coli, a type of bacteria commonly found in the intestinal tracts of humans and animals. Though most forms of E. coli are harmless, some strains can make humans sick.

E. coli likely got into the Seine a few different ways, according to William Schaffner, MD, an infectious disease specialist and professor at the Vanderbilt University School of Medicine.

“One is just run-off from the banks that go into the water,” Schaffner told Health. “That can carry fecal material from animals like dogs and cats into the water.”

Heavy rainfall is also a big factor. With large amounts of rain, sewage systems run the risk of becoming overloaded and overflowing. “That contaminated water that’s supposed to stay in the sewer system ends up contaminating the [clean] water,” Thomas Russo, MD, professor and chief of infectious disease at the University at Buffalo in New York, told Health. That water from the sewer system, in turn, makes E. coli levels rise.

Swimming in water contaminated with E. coli raises your risk of infection, which can cause gastrointestinal symptoms like abdominal cramps, diarrhea, nausea, and vomiting. But water can be home to a host of other contaminants. “You can become ill from a variety of bacterial and viral infections,” Schaffner said.

Other illnesses that can result from swimming in contaminated water include:

The biggest way people can get these illnesses in the water is by accidentally swallowing contaminated water, said Russo. “It’s very hard when you’re swimming not to get small, microscopic doses of water in your mouth,” he explained. The exact amount it would take to make you sick depends on the bacteria and concentration in the water.

While gastrointestinal illnesses are the most common issue people can face after swimming in contaminated water, Schaffner said that skin rashes and eye infections can also happen.

It’s important to note that water contamination isn’t specific to the Seine—it can happen nearly anywhere. “This occurs in all bodies of water. All water has some level of fecal contamination,” infectious disease expert Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security, told Health. “The danger arises when it exceeds a certain threshold level.”

Water testing is common in the U.S. to look for levels of E. coli and other bacteria in the water, Schaffner said. But this is generally done on a state and local level, and the agencies that oversee this testing vary by region.

Typically, local health officials will post signs at a beach or swimming area that clearly state that the water is not safe for swimming. However, you can also usually check the website of your state’s department of natural resources for detailed information about the water quality in an area where you’re interested in swimming, said Schaffner.

As a general rule, if health officials say that the water is not safe to swim in, you should take a pass. “I do not recommend swimming in contaminated water,” said Schaffner.

Even water without a contamination warning may not be 100% safe. "Just assume," said Adalja, "that when you're swimming in a body of water, that there is some level of fecal contamination."