Why is the Seine unsafe for Olympic triathlon swimmers?

The men's Olympic triathlon planned for Tuesday has been postponed over concerns about water quality in Paris' Seine river, where the swimming portion of the race was supposed to take place.

The event has been postponed to Wednesday, which is the same day the women's competition is also scheduled to take place. However, both events are subject to water tests demonstrating that the Seine is safe to swim in.

Questions also remain about the women's and men's 10-kilometer (6.21-mile) marathon swimming races, which are due to be held in the Seine on August 8 and 9.

Water contamination in the Seine has been a controversial topic in recent weeks. A triathlon training session due to be held in the Seine was cancelled on Monday, which is the latest event to be scuttled by water pollution.

#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, causing swimmers during the 1924 Paris Olympic games to compete 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 have been working 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 first-hand.

Seine E. coli levels a health concern

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

Recent rainfall over Paris has 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 that the heavy rain over Paris on Friday and Saturday had compelled them to "reschedule the event 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 are not the only concern, however. Leptospira, transmitted by rodent urine, can be found in contaminated water and can cause severe kidney disease.

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

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

Seth Rider, one of 55 triathletes entered in the men's race, has been taking 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 Saturday.

"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 (née Snowsill), an Australian triathlon athlete, retired in 2014 after struggling with health problems related to swimming in polluted water at a World Cup event.