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Paris – In the debate about the water quality of the Seine River during the Olympic Games in Paris, criticism of those responsible is increasing. The main issue is the lack of transparency in the measured values. According to media reports, several swimmers are said to have fallen ill, but so far no connection to the competitions in the Seine has been confirmed.

The French online portal Media part Last Wednesday evening, the French daily published alleged official data (behind a paywall) of samples from the Seine, which, according to the media, show largely inadequate water quality since the start of the Olympic Games.

Only on July 30 and 31 were the values ​​within the limits, with measurements available up to August 5. The standards applied were those of the World Triathlon Association, writes Mediapart. If the standards that apply to the general public were applied, the Seine would have been even less suitable for swimming.

The focus is on the concentrations of two bacteria in the water: Escherichia coli (E. coli) and intestinal enterococci. These are considered indicators of water contaminated with faeces. The Seine is being sampled at several locations.

The international water sports association World Aquatics, for example, states in a manual that the water quality of rivers is unacceptable if E. coli levels exceed 1,000 colony-forming units per 100 milliliters and enterococci exceed 400/100 ml. According to data published by Mediapart, there were peaks on individual days for E. coli levels of well over 2,400 and for enterococci of more than 1,400.

According to the association, tests for intestinal bacteria are only one factor in water quality controls. More subjective indicators such as the appearance of the water – such as color, garbage, algae blooms – and the weather forecast are also taken into account.

A request from the German Medical Journal at Paris 2024 regarding the media report initially remained unanswered. Media part reported that the city of Paris did not respond to a request for information about the results and that the organizing committee only disputed the journalists’ interpretation of one measurement, which was only slightly above the limit and was only obtained next to, not directly on, the triathlon course.

Warnings of poor readings already in spring

The Surfrider Foundation, which claims to have taken samples from the Seine more than a dozen times before the Olympics and no longer has permission to do so, demanded full transparency from the organizers in a statement yesterday in response to the French media report.

In April, the NGO had already warned in an open letter, citing its own analyses, of the Seine’s poor cleanliness and the risk of illness for athletes. It says it has been committed to the health of water sports enthusiasts for decades.

The city of Paris regularly published information on E. coli and enterococci levels on its website before the games began, but no longer does so. Instead, it states that only the organizers provided data on the water quality of the Seine during the games. The Surfrider Foundation, however, criticizes the official information as inadequate and imprecise.

Several athletes fell ill

In recent days, media reports have revealed several cases of illness among athletes from different nations who had, for example, swum in the Seine during a triathlon.

The Belgian triathlete Claire Michel, for example, wrote on Instagram, citing blood tests, that she had caught a virus, had diarrhea and vomiting for three days and spent a day in the hospital. As in the other cases, a direct connection to the Seine has not been confirmed. There was also speculation about food as a possible cause.

The open water swimming competitions over ten kilometers were only held yesterday and today. A Swedish athlete did not even take part today because of concerns about the water quality and the large amount of water that one would swallow during a race lasting almost two hours, according to the Reuters news agency. The organizers claim that the water is being closely monitored and that the values ​​at all measuring points yesterday were very good.

The World Triathlon Association itself states in a paper on water quality that it is generally difficult to prove whether illnesses are actually the result of exposure while swimming. The symptoms are often non-specific and the illness is often not diagnosed accurately. There are many different viruses that could cause illness, but there are no routine tests for them.

The document also points out that several physiological mechanisms during exercise could make athletes more vulnerable, such as the hormonal stress response. Infections can occur through swallowing water, but also through the mucous membranes and skin.

Also a question of methodology

A company that claims to have been studying the water quality of the Seine at a bathing area in cooperation with the city of Paris for years has, according to a Mirror-The report also concluded that the Seine was too dirty for the triathlon.

However, more advanced methods were used here, which, in contrast to urban laboratory methods, made it possible to detect not only free-floating bacteria, but also bacteria bound to particles.

The Paris City Hall told the Mirror According to, that the company’s method is not a substitute for official data “which has been jointly validated by all parties involved”.

The bacterial contamination in the Seine has been a topic of discussion in the French capital for weeks. After heavy rainfall on the day of the opening ceremony, the limit values ​​for E. coli bacteria in the river were initially exceeded, some training sessions were cancelled and a competition was also postponed.

One of the problems is the combined sewerage system for wastewater and rainwater, which can overflow during heavy rainfall. To counteract this, a 50,000 cubic meter underground retention basin was built at Austerlitz station as part of the Olympic preparations.

Paris has invested around 1.4 billion euros in these and other measures to keep the Seine clean. Mayor Anne Hidalgo recently went there herself to promote the flagship project.

From summer 2025, everyone will be allowed to swim in it – in newly constructed outdoor pools. Swimming in the Seine was forbidden for more than a hundred years. © ggr/aerzteblatt.de