Marathon Swimming Held at Olympics But Concerns About Seine Water Safety Remain

After months of uncertainty and canceled training sessions, the women’s marathon swimmers dove into the Seine on a sunny morning under the Pont Alexandre III on Aug. 8.

Two days before the race, a training session designed to help familiarize swimmers with the 1 mile (1.67 km) course that they swim six times was canceled due to unsafe levels of enterococcus bacteria. The decision was made by World Aquatics, which oversees the sport, and officials with Paris 2024. Enterococcus is associated with fecal contamination.

The training was rescheduled and held the day before the race, and most swimmers took advantage of the opportunity, but had to weigh the risk of becoming ill just before the main event, with the chance to strategize about the best lines to follow in the water to maximize speed and conserve energy in the 10 km race. “Our first training session got canceled, and then the second time, we didn’t really want to spend too much time here, risking getting sick before the race,” said Katie Grimes of the U.S., who finished in 15^th place. “So I really didn’t get too much time in here before.”

Most marathon swimming events are held in lakes, bays or oceans, and the river location introduced another variable for swimmers to navigate—the current. The first portion of the lap took swimmers from Pont Alexandre III, which connects the famed Champs-Elysees area to the Eiffel Tower region, and under Pont des Invalides before they turned at Pont de l’Alma. It followed the river’s current, which can flow from 2 to 3 mph (3.2 to 4.8 kmh), while in the back half of the lap, swimmers fought it.

Read More: What Olympic Triathletes Thought About Swimming in the Seine

Training sessions are important for open water contests, especially in a river. In the Seine, swimmers also tried to navigate swimming close to the banks of the river for the most efficient line, although some portions contained vines that brushed their arms with every stroke.

“That was the hardest thing I’ve ever done, and the current—that’s something I’ve never done before,” said Grimes, who also competed in the pool and earned silver in the 400-m individual medley. “That required a completely different mindset going into the race [because] it was changing the entire time I was racing.”

Experience in navigating currents and taking advantage of the boost they can provide helped Sharon Van Rouwendaal from the Netherlands, who also won the event at the 2016 Olympics and earned silver at the Tokyo Games, finish first in Paris. Silver medalist Moesha Johnson of Australia, who trains with Van Roudenwaal, led with a fast start, and then maintained that lead through the third and most of the fifth laps, but was eventually outpaced by Van Rouwendaal in the last half of the fifth lap. Italy’s Ginevra Taddeucci, who finished 22d at the 2024 world championships, was the surprise bronze medalist after keeping pace with Van Rouwendaal and Johnson throughout the six laps.

“The current was a big, big challenge,” said Johnson. “And it really changed the way that you had to sit in the pack—there wasn’t really a pack. I definitely went to the front earlier than planned.”

Not being able to train in the Seine itself made strategizing the race more challenging, said Mariah Denigan, Grimes’ teammate from the U.S. who finished 16^th. “Going into it, we usually have a more swims, and I feel like that would have definitely helped a little bit had I had more experience being able to swim with the current.”

And it wasn’t just the current they had to worry about. “It was really hard because we couldn’t really focus on the race,” said Bettina Fabian of Hungary, who finished fifth. “We had to care about the [water] quality, and what’s going to happen afterwards. We [had to] focus on not swallowing water and [being] safe in the race. I saw some brown things; I hope it’s not what I thought it was. I am concerned, but I brought some Hungarian palinka [fruit brandy] so I hope I’m not going to get sick after [the race].”

Taddeucci echoed the concern that’s become a distraction for the marathon swimmers, especially after taking part in the training session the day before the race. “Of course I’ve swum in better places,” she said. “I was only caring about not feeling sick, but It was fine.”

Read More: Which Olympic Sport Is Hardest on the Body?

The triathlon was also held in the river in the first week of the Paris Games, and the Belgian team withdrew from the mixed relay after one of its athletes, Claire Michel, was reportedly hospitalized after becoming ill, according to Belgian newspaper De Standard, although World Triathlon or Olympic officials could not confirm what caused her sickness. The men’s triathlon was postponed by a day because of unsafe conditions.

Why the uncertainty over the water quality? Experts say the levels of bacteria, primarily E. coli and enterococcus, fluctuate depending on the amount of rainfall and sunlight hitting the water. With heavy rains, the excess water overwhelms water treatment plants and the overflow seeps into the Seine. Ultraviolet light can help to kill off some bacteria.

Leading up to the women’s swimming marathon, dry, sunny days helped to keep the water at safe enough levels to hold the training run on Aug. 7 and the race on the following day. But it will take a day or so before the swimmers will know if the water was really safe. “I did swallow a lot of water so I’m hoping that I’m okay,” said Grimes.