Is the Seine Clean Enough? Olympic Triathletes Wait on Testers.
The promise was they would swim in the Seine.
So far this year, no Olympian has been able to do so.
After the heavy rains on the weekend, swimming officials at the Paris Games have canceled both familiarization swims for triathletes eager to try out the river before the men’s and women’s individual events set for this week. Each time, poor water quality levels were blamed.
Better news arrived on Monday: Paris 2024 organizers say the hot sun over the past two days most likely means the water will be clean enough on Tuesday morning for competitors to dive in for the first 1.5 kilometers of the men’s race before jumping on their bicycles and then running 10 kilometers.
“We are confident we will be able to hold the competition tomorrow,” Etienne Thobois, the chief executive of the Paris 2024 organizing committee, said at a news conference on Monday. “We have done everything we can to achieve the swimmability of the Seine.”
The city of Paris and its mayor, Anne Hidalgo, in particular, have a lot riding on that promise, and the sight of athletes splashing down the river with the gold dome above Napoleon’s tomb glittering nearby and the Eiffel Tower rising ahead.
The authorities have spent 1.4 billion euros (more than $1.53 billion) on an ambitious, multipronged and labor-intensive plan to clean the Seine — or, more precisely, to prevent filthy water from flowing into it.
They have dug new sewage pipes to homes, connected the city’s refurbished peniches — houseboats — to the sewage system and added special treatments to two upstream sewage plants.
In May, they opened a giant underground water storage tank on the city’s left bank that can hold 13.2 million gallons of rainwater: enough to fill 20 Olympic pools. It is one of five big engineering projects built to hold rainwater during storms — water that was previously dumped into the Seine — so it would not overwhelm the city’s antiquated sewer system.
The result has been a big drop in two indicator bacteria — E. coli and intestinal enterococci — that can cause illness in humans, often meeting the threshold set by the European bathing directive. But that effort was not just to ensure triathletes and open-water swimmers could compete in the river this summer.
The problem is rain. When it falls heavily, as it did in Paris during the opening ceremony on Friday and the first official day of Olympic competitions on Saturday, water runs off the city’s concrete roads and sidewalks into the river, and some upstream sewage systems are incapable of dealing with the increased volume.
And for the next day or two after the rain showers, test results in the Seine show a spike in bacteria levels. But as long as the rain subsides, those bacteria are devoured by other organisms in the river, Jean-Marie Mouchel, a hydrologist and professor at Sorbonne University, explained in an interview this spring.
“It’s a weather question,” said Mr. Mouchel, who has studied the Seine for three decades. “If the weather is nice, if the flow of the Seine is calm, if there are no storms, the water quality is good.”
Recent test results posted weekly by the region are so promising that even critics like Surfrider, an environmental conservancy organization, are singing Paris’s praises.
“The city has done a lot of things,” said Marc Valmassoni, Surfrider’s water and health coordinator. “We hope many other cities like Bordeaux, Toulouse, Nantes, will have the same idea and over the next few years make their urban rivers swimmable.”
The decision about whether triathletes dive in the Seine near the Alexandre III bridge on Tuesday will be made around 4 a.m. Paris time, when World Triathlon delegates meet with the local authorities and Paris 2024 officials to examine the most recent results.
“Athletes will find out when they wake up: They will know if they should stay in bed or get up and go for breakfast,” said Benjamin Maze, the high-performance manager for the French Triathlon Federation. But to them, that is routine.
“This is a sport based on adaptation,” Mr. Maze said. “They are used to responding to weather conditions. They are focused on what they can control — their fitness and preparation for the event.”
They also have been well briefed about the currents, which are high, he said. And many, including the American Morgan Pearson and France’s Dorian Coninx, both medal contenders, got to test out the Seine in a race last summer.
Their feedback at that time would make Ms. Hidalgo happy.
“They were amazed by the course,” Mr. Maze said. “They had goose bumps.”
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