Water quality was acceptable when Olympians swam in Seine River, data shows

Water quality data used by Paris Olympics organizers shows that bacteria levels in the Seine River were within acceptable levels on the days that athletes swam in the famed waterway, according to their tests and established thresholds.

The Associated Press obtained the results of daily tests for the fecal bacteria E. coli and enterococci on water samples taken at four points in the river two or three times daily. The data spans a period from July 19, a week before the opening ceremony, through Wednesday, when marathon swimmers dove in to test the course where they would race Thursday and Friday.

Officials have been sharing some water quality data at briefings during the Games, but the new information is a more complete set of numbers, including the results from at least two tests each day for all four sampling sites.

The river that flows through the heart of France's capital has been so polluted that swimming has been banned for a century with a few exceptions. Paris launched massive infrastructure improvements costing 1.4 billion euros ($1.5 billion) to ensure the Olympic triathlon and marathon swimming events could be held in the Seine.

Officials claimed success after the competitions went forward largely as planned.

But the data shows that the bacteria levels were much higher than are deemed acceptable for competition on many days over the three-week period, generally registering as “poor” for three or four days after heavy rain fell. That raises questions about Paris' long-term plans to allow the public to swim in the river beginning next summer.

Weather has an enormous effect on the Seine's cleanliness. Rain can cause runoff and wastewater — and, therefore, bacteria — to flow into the river. On the flip side, warm temperatures and the sun’s ultraviolet rays can kill the germs. Hot and sunny weather during the Games has occasionally given way to drenching rain.

Elevated bacteria levels following downpours caused the cancellation of some test runs meant to allow athletes to familiarize themselves with the course ahead of both triathlon and marathon swimming events. They also resulted in the men's individual triathlon being delayed by a day, but otherwise, the Olympic events were held as planned in the river.

Several athletes who swam in the Seine reported gastrointestinal illnesses after their events, but it wasn’t clear whether bacteria in the water were to blame.

There were notable downpours during the Games' opening ceremony on July 26 and the night of July 31, after the individual triathlon competitions were held earlier that day. Each time, the bacteria levels in the river increased dramatically and took several days to dip back below the level deemed acceptable, the data shows.

The numbers reveal how levels can differ from one testing site to the next, even though all the areas are relatively close together.

On Monday, when the triathlon mixed relay was held, all four sites had acceptable levels for E. coli, while the enterococci level was too high at one site. But that site, the Port du Gros Caillou, was outside the relatively short course used for the relay.

Under guidelines set by World Triathlon and World Aquatics, the two sports’ governing bodies that decided whether the Olympic events would go forward each day, “good” water quality can include up to 1,000 colony-forming units of E. coli and up to 400 colony-forming units of enterococci per 100 milliliters.

The bacteria levels can change remarkably in a short amount of time. The Port du Gros Caillou site registered a “poor” level of 436 units of enterococci at 5:45 a.m. Monday. At 12:25 p.m., it showed a “very good” 99 units.

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 infections in the urinary tract or intestines. Several factors determine whether a person falls ill after exposure, chief among them a person’s age and general health.

___

AP Olympics: https://apnews.com/hub/2024-paris-olympic-games