Olympic Games: Marathon swimming training, cancelled the day before, was able to take place in the Seine

This article was originally published in English

The verdict is in: the Olympic marathon swimming event will take place in the Seine after a training session intended to allow athletes to familiarize themselves with the course was cancelled on Tuesday, August 6, due to the water being deemed too polluted.

According to the newspaper L’Équipe, a meeting on the quality of the river was held early on Wednesday, in the presence of representatives of World Aquatics, and new tests carried out confirmed that the training session would take place cancelled the day before.

The big rehearsal is underway this Wednesday morning: from 7:30 a.m. to 9:30 a.m. The women’s and men’s events will take place on Thursday and Friday.

Swimmers in the marathon swim, sometimes called open water swimming, will do six laps between the Pont Alexandre III and the Pont de l’Alma for a total of 10 kilometers.

Five training sessions have been cancelled since the start of the Olympic Games. The cause is the concentration of two types of bacteria present in the faeces: Escherichia coli (E. coli) and the enterococci.

Most strains of E. coli and enterococci are harmless, and some live in the intestines of healthy people and animals.

But others are dangerous, and even a mouthful of contaminated water can cause urinary tract or intestinal infections. Several factors determine whether a person becomes sick after exposure, including age and general health.

Four triathletes – out of the 100 or so who took part in the men’s and women’s individual races last week – fell ill in the days that followed, without it being known exactly whether water was the cause.

Enterococcus levels recorded on Monday were available mid-morning on Tuesday and, although they show an improvement in the quality of the Seine water, one of the four tests still did not meet standards.

According to World Aquatics and World Triathlon guidelines, water of “good quality” may contain up to 1,000 colony forming units of E. coli per 100 milliliters and up to 400 colony forming units of enterococci per 100 milliliters.

Data released Tuesday show that a sample taken early Monday at Port du Gros-Caillou, which is on the course of the marathon swim but beyond the point where the triathletes turned around Monday, revealed a level of 436 units of enterococci.

A century of prohibition

With a few exceptions, swimming in the Seine has been prohibited since 1923 due to excessive pollution.

Paris has implemented an ambitious 1.4 billion euro swimming plan, led by the State, to allow certain swimming events to be held in the river.

These included building a giant basin to collect excess rainwater and prevent wastewater from flowing into the Seine, renovating sewer infrastructure and modernizing treatment plants.

The water quality of the Seine is closely linked to weather conditions. Heavy rainfall can cause pollutant-laden sewage and runoff to flow into the river, resulting in high levels of faecal bacteria, while high temperatures and the sun’s ultraviolet rays can kill pathogens.