Swimming at the Olympics began before pools were used

At Athens 1896, Paris 1900 and St Louis 1904 (the first three modern Olympic Games), all swimming events were held in a natural body of water.

Pools were then exclusively used for swimming in Olympic related events (except Triathlon) until 1991 when Marathon Swimming was held in Perth, as part of the FINA World Swimming Championships for men and women. Both events required athletes to swim 25km, whereas in Paris it will be a 10km race.

The 10km distance was added in 2001 in Fukuoka, Japan, where the 2023 World Championships were held at which Australian Chelsea Gubecka won the silver medal.

Paris will use the Seine River for Marathon Swimming

Two marathon swimming events, a men’s race and a women’s race, will start and finish in the Seine River. Athletes must complete a 10km course, with the women competing on the 8th of August and the men on the 9th at 7:30am local time.

The French government has been working to improve the water quality of the Seine river, with swimming in the Seine having been banned since 1923 because of pollution. A €1.4 billion project ($2.35 billion) is in operation to have the Seine ready for the Olympic competition.

The strategies and challenges at play

The race features a mass start, where competitors dive in from a platform simultaneously at the sound of a tone with no lane restrictions. As such, incidental contact between swimmers is permitted.

Athletes wear a wristband known as a transponder, which keeps track of their timing in the results system. It will take athletes nearly two hours to finish, with an athlete’s ability to adapt to tides, current changes all factoring into their swim.

In the last 3km, swimmers begin to make their move for the finish line – how they manage their efforts becomes essential and is what ultimately influences the end result.

Athletes must touch a pad at the end of the race to stop the clock, and can be disqualified for slipstreaming, pacing (with a safety craft or other person), walking or jumping, or finishing without their transponder.

Chelsea Gubecka’s breakthrough

It was 10 years after Australian Chelsea Gubecka made her World Championships debut as a 14-year-old that she won her first World Championships medal, silver, in Japan earlier this year.

“It's a long time coming, but I'm just sort of starting to get into my group now. I feel like I'm a little bit older and getting wiser by the second,” Chelsea said post-race.

“I think over the years, I have learned to embrace the challenge of racing and also how to relax, to keep the heart rate down and stay very calm.”

Water temperature requirements

The water temperature for Olympic marathon swimming should be a minimum of 16°C and a maximum of 31°C. The minimum depth of water at any point must be 1.40 metres.