An ambition from Paris Olympics organisers to cut the carbon footprint of catering at this year's eco-friendly Games has run into a problem: the huge appetites of meat-loving athletes.

Ecuador's Brian Pintado won the first athletics Olympic gold medal of the Paris Games on Thursday with victory in the men's 20-kilometre walk.

Defending champions Canada reached the quarterfinals of the women's Olympic football tournament on Wednesday thanks to a 1-0 win over Colombia in Nice hours after they had an appeal against their six-point deduction dismissed.

Rafael Nadal admitted he may have played at Roland Garros for the final time after he and Carlos Alcaraz were dumped out of the Olympics men's doubles on Wednesday.

There will be 18 gold medals up for grabs in France, including four each in rowing and swimming, plus two each in judo, sailing and athletics, while Olympic champions will also be crowned in shooting, artistic gymnastics, and fencing.

Pan powered to the finish in 46.40sec, beating the world record time of 46.80 he had set in February in Doha. It was China's first swimming gold of the Paris Games.

American great Ledecky again set new standards, cementing her reputation as the greatest distance swimmer the sport has known.

Nadal ends the Games without the third Olympic gold medal he craved on what could well be his last appearance on his beloved Parisian clay.

The Frenchman will also go for gold later on Wednesday in the 200m breaststroke.

When doctors x-rayed his spine after the crash in 2021, "they said maybe I'll never walk normally again," an emotional Lind told AFP after his win on Wednesday.

For Ni, a former world champion with China who now represents Luxembourg, her stint in Paris was a dream come true.

"The Chinese train so hard, the way that they train, everything is close to perfection," the Briton said.

"I'm soaking wet, honestly," he said. "It's a very, very humid day as it was yesterday. I just hope it rains so it cools down the temperature a bit and the air," said Djokovic.

"She has given up her place in the 100 metres ... all the information that we can provide is that she is not going to participate in the 100 metres," Watts, Jamaica's track and field team manager, told Reuters.

"I can't find the words, it's crazy what's happening to me. This morning, I would never have believed it," Beaugrand said.

Nuclear-armed North Korea declared the South its principal enemy earlier this year and tensions between the two countries are at one of their highest points in years.

Five medals will be on offer in the swimming at La Defense Arena, including the men's 100 metres freestyle, 200 butterfly, 200 breaststroke and the women's 100 freestyle.

Adding to the early criticism about the quality and quantity of the food at the Olympic Village, the queen of gymnastics gave the French offerings there a thumbs-down, opining that athletes would need to get out to enjoy the "real" local cuisine.

The men's and women's triathlons were given the green light a day after the men's event had been postponed because of pollution levels in the Paris waterway.

On Tuesday, McKeown retained her 100m backstroke crown from Tokyo, crushing American rival Regan Smith to earn her fourth Olympic gold medal and join a select group of swimmers with three individual titles.