Here’s what you should know about the Seine River’s water quality during the Paris Olympics

Swimming is prohibited in River Seine, long polluted in Paris for more than a century. So, with the Olympic swimming events planned for the river, the city invested 1.5 billion dollars (1.4 billion euros) to try to clean it up.

With the Paris Games underway, authorities are keeping an eye on water quality. Athletes may experience health effects from swimming in a river with higher than permitted levels of E. coli or other bacteria.

Here are some important things you should know:

Paris, like many ancient cities around the world, has a combined sewer system, meaning the city’s wastewater and stormwater flow through the same pipes. With heavy or prolonged periods of rainpipes can become overloaded and untreated wastewater flows into the river instead of to a treatment plant.

That could mean bacteria, viruses or parasites get into the water, said Dr. Nicole Iovine, an infectious disease specialist at Florida Health University in Gainesville. And it’s not just human waste.

“It’s also wildlife – rodents, for example. When it rains a lot, all these animals can end up in the Seine,” she said.

To prepare for the Paris Games, the city built a giant basin To capture excess rainwater and prevent untreated waste from flowing into the river, it renovated the sewage system and modernized water treatment plants.

Heavy rain can still flood the system.

“The city of Paris has worked hard to clean up the Seine, but it can’t control the weather,” Iovine said.

Rain on the opening weekend of the Olympics filled 20% of the basin, so contamination levels after it likely came from wastewater upriver, city officials said.

Water quality tests conducted in June revealed unsafe levels of E. coli bacteria, although results in early July showed improvements. E. coli is found in the digestive tract and waste of humans and animals. Most strains are not harmful, Iovine said, but high numbers could indicate dangerous bacteria.

A monitoring group does daily four-point testing for E. coli, as well as enterococci bacteria, which can flag fecal matter and potentially disease-carrying germs.

The World Triathlon Federation has considered E. coli levels greater than 900 colony-forming units per 100 milliliters to be unsafe.

But it’s not a “magic” number, Iovine said, and authorities likely take it into account. factors – such as weather — when making decisions about water quality.

On a sunny day, the sun’s ultraviolet rays can kill bacteria and lower levels.

Swimming in water with dangerous levels of bacteria can cause stomach upset and intestinal problems. Swimmers can inadvertently swallow water or contract infections through open cuts.

Even a sip of contaminated water can cause diarrhea, and the germs can cause illnesses such as urinary tract or intestinal infections or, in the worst case, life-threatening sepsis.

“The athletes are young and in the best shape ever, so they will be more resilient than many of us,” Iovine said. “But that doesn’t mean they can’t get sick from these things.”

___

Bose reported from Jackson, Mississippi. AP reporter Kate Brumback contributed from Paris.

___

The Associated Press Health and Science Department receives support from the Robert Wood Johnson Foundation. AP is solely responsible for all content.