Water contamination in the Seine River was a controversial topic right up to the opening ceremonies at the 2024 Paris Olympics.

It was deemed safe on July 17, 2024, and opened for swimming for the first time in about a century. A women's swimming event went ahead, but was followed by the news that a men's event was to postponed and rescheduled.

Then, Olympic swimmers started to get sick. 

#JeChieDansLaSeine

Pollution in the Seine is no new controversy — swimming in the river has been illegal for more than 100 years due to health concerns. The first ban came into effect in 1923, leading to swimmers during the 1924 Paris Olympic games competing in swimming pools.

Most of the city's wastewater has been flowing into the Seine since the ban came into effect. Leaking and overflowing sewage systems are the main source of pollution.

French authorities worked to clean up the water for the 2024 Paris Olympic Games, spending €1.4 billion ($1.5 billion) on improving water quality.

The goal was to cut bacterial contamination by 75% before the first Olympic swimming event, but the city has so far been unsuccessful in quelling the concerns of athletes and local Parisians.

Parisians disgruntled at the project's costs pledged to protest poo in the Seine en masse, led by #JeChieDansLaSeineLe23Juin, which translates as # I shit in the Seine on June 23.

Despite this campaign, Paris Mayor Anne Hidalgo swam in the river earlier in July in a bid to demonstrate the Seine's cleanliness firsthand.

Seine E. coli levels a health concern

Water tests from the Eau de Paris monitoring group over the last few weeks have shown levels of Escherichia coli (E. coli) in the river were significantly higher than is safe for humans.

Rainfall over Paris made the issue worse — heavy rains often cause levels of E. coli and other bacterial colonies in rivers and lakes to rise.

In a statement, organizers said heavy rain over Paris on the first weekend of the Games had compelled them to reschedule events "for health reasons."

E. coli is often linked to fecal matter in water and can indicate contamination from sewage. Even a mouthful of contaminated water containing high levels of E.coli can lead to diarrhea, urinary tract infections, pneumonia or sepsis. Skin rashes and ear or eye pain are also common.

Waterborne diseases

E. coli infections aren't the only concern, however. Leptospira, transmitted by rodent urine and which can also be found in contaminated water, can cause severe kidney disease.

Infections from other waterborne bacteria like cyanobacteria and enterococci can also result in gut-related health problems.

And then there are parasites such as cercarial larvae, often found in water populated by waterfowl, which can cause itchy skin rashes.

Seth Rider, one of 55 triathletes in the men's race, took unconventional measures to prepare for exposure to bacteria.

"We know that there's going to be some E. coli exposure, so I just try to increase my E. coli threshold by exposing myself to a bit of E. coli in your day-to-day life," the US athlete said in a press conference on July 30.

"Just little things throughout your day, like, not washing your hands after you go to the bathroom and stuff like this," he said.

Other Olympic athletes have suffered long-term from swimming in contaminated waters, however. Emma Frodeno (formerly Emma Snowsill), an Australian triathlon athlete, retired in 2014 after struggling with health problems related to swimming in polluted water at a World Cup event.

Edited by: Timothy Jones

This article was originally published July 30, 2024, and updated August 5, 2024 to include the news of Olympic athletes getting sick.