The organizers breathed their first sigh of relief when the green light was finally given at 3:30 am, just a few hours before the first swimmers were due to jump into the water. On Wednesday, August 16, at 8 am, around 100 triathletes were allowed to dive into the Seine from a pontoon set up at the foot of the Alexandre-III bridge. Their aim was to scout the course during a competition scheduled until August 20 as a practice run for the 2024 Paris Olympics.

The elite athletes were the first to be officially allowed to enter the river since numerous projects were launched in 2016 to make it swimmable again. If all goes well − if the weather forecast holds and no major storms hit the Paris region between now and then − 80 paratriathletes will also get to familiarize themselves with the river's ebbs and flows on Friday before competing in a full race this weekend.

On Monday, less than 48 hours before the start of the event, doubt hung in the air as to whether it would even proceed. Thunderstorms were gathering, and heavy rainfall at the beginning of the weekend had worsened the water's bacteriological readings. The same reasons had led to the cancellation of an Open Water Swimming World Cup event on the weekend of August 5 and 6, which was also intended as a pre-Olympics trial run. In late July, the authorities explained that Paris had seen the heaviest rainfall in 20 years. Sewage systems were overburdened. When that happens, the overflow is discharged into the river.

The city of Paris nevertheless assured the water quality was good. But during the night-time meeting where a decision had to be taken, the regulatory data used by the event organizer to make the decision was clear: The concentration of Escherichia coli − the micro-organisms indicating the presence of fecal contamination − was above the authorized threshold (1,000 colony-forming units per 100 ml of water), meaning the competition could not go ahead. On the same first weekend in August, 57 triathletes fell ill after competing in an event at the World Triathlon Championships in England.

With less than a year to go before the opening ceremony, these risks and uncertainties are a reminder of the huge challenge the 2024 Paris Olympics teams set themselves by organizing the 10-kilometer marathon swimming race and the triathlon and paratriathlon events in the heart of the capital. But staging them at the foot of one of Paris' most beautiful bridges, between the Grand Palais and the Eiffel Tower, undeniably makes for a spectacular setting.

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