Paris, France - France and Britain dominated the podiums in the Olympics triathlon on Wednesday, which finally began in the Seine after days of suspense over whether the river would be clean enough for racing.

Cassandre Beaugrand took the women's gold ahead of Switzerland's Julie Derron and Britain's third-placed Beth Potter.

In the men's competition, which had to be delayed by 24 hours after the Seine failed water tests, Alex Yee stormed to a dramatic victory by passing rival and friend Hayden Wilde from New Zealand in the final stretch.

Frenchman Leo Bergere finished third.

"I started to find my legs with about 3k to go, and I said to myself, 'I'll give myself one last chance to make this happen,'" Yee told reporters of his late surge, adding that British legend Alistair Brownlee had shouted him on during the last lap.

All the attention during the build-up had been on the Seine, which was the centerpiece of a spectacular course that included a biking and running route through the historic heart of the French capital.

The Seine has been too dirty for swimming all week after Paris was deluged by rain during the opening ceremony of the Games on Friday, with the equivalent of a month's rain falling over 36 hours.

The storms overwhelmed the city's sewerage system despite a recent $1.5 billion upgrade, leading to discharges of untreated wastewater that sent E.Coli bacteria levels spiking.

Beaugrand said she "never doubted" that the swimming would go ahead despite warnings that it might be canceled, which would have turned the triathlon into a duathlon of only cycling and running.

"It would have been shameful for our sport... it would have been a disgrace," she told reporters afterwards.

After the competition was given the go-ahead at around 4 AM, thousands of fans turned out to line the streets, which were slippery and hazardous during the women's race after overnight showers.

Beaugrand was in contention from the start, remaining in touch with front-runner and defending Olympic champion Flora Duffy during the swim when many competitors reported being surprised by the strength of the river currents.

The UK-based 27-year-old had vomited before the start, finding comfort in words from fellow competitor Georgia Taylor-Brown from Britain, the silver medalist at Tokyo 2020, who helped settle her nerves.

"She told me 'It's just a race, you can do it'," Beaugrand, who grew up near Paris but moved to Britain in 2023, told French television.

After so much public debate about the water quality, Hayden said the currents were the biggest concern.

"I watched the women's race beforehand and was like 'wow'," he told a press conference.

The triathlon in the Seine, followed by marathon swimming next week, were both intended to highlight efforts made by French authorities to clean up the waterway, which has been off-limits for Parisian swimmers since 1923.

Due to an exceptionally wet spring and early summer, the Seine had been consistently failing tests until the start of July.

Levels of the E.Coli – a key indicator of fecal matter – had been 10 times higher than authorized triathlon limits on some days in June.

More rain had threatened to force another delay to the schedule overnight on Tuesday-Wednesday, but deputy Paris mayor Antoine Guillou told AFP that there had been no discharges from the sewers.

"The rain was quite light and low in quantity," Guillou, who is in charge of public sanitation, told AFP.

But water charity Surfrider said it remained "worried that athletes began their triathlon race this morning at 8 AM even though it rained for several hours before the start," adding that it awaited the publication of full resullts.

"I'm definitely going to be visiting the bathroom later," South African Jamie Riddle, who finished 25th, joked to reporters. "I swallowed gallons and gallons of water, so that's going to be a fun, post-race party."