Not all swimming events are the same. Miles away from the futuristic Aquatic Centre, with its parallel lanes in the sanitised pool, there is the Serpentine. The great old lake, at the heart of Hyde Park, is the location for the 10km race on 9 August. Twenty-five athletes will swim six laps of it, through the ducks and the reeds, in pursuit of gold. At the front should be Keri-Anne Payne, Britain's two-time world champion in the 10km open water, who would clearly not want to be anywhere else.
"It's not the most glamorous of sports but that's fine, we all know that and we're all prepared for that when we get in," Payne said yesterday. She had just been training in the Serpentine, and said that its very English challenges were by no means the most unpleasant she has faced.
"I can assure you that as an open-water swimmer I've swum through way worse things than reeds and a few ducks. It just depends on the person and how strong-willed you are. I'm glad I did it today to get my first taste of swimming round it and swimming hard through the reeds as well, just to see how they were. It was great."
While the conventional swimming events take place in a controlled environment, not very different from one aquatics centre to the next, open-water demands flexibility to the surroundings. "I've been through a couple of interesting open-water swims," Payne recalled. "The 2007 World Championship in Melbourne, my first one, was in St Kilda, just off the beach. There were thousands and thousands of jellyfish, all the size of dinner plates. And it was pretty difficult, to be honest. It took a lot of mental strength for me to get in there and swim.
"In final preparation I swam maybe 300 metres before I completely freaked out and had to be pulled out. But I knew that if I wasn't there somebody else was happily going to step into my place. So open water really shows you how to be tough and how to handle that kind of stuff."
There was another sea-life scare. "Another one was swimming in Hong Kong, an absolutely beautiful location, and we swam past these big buoys, and I asked what the buoys were, and they were for shark nets. We were swimming on the side of the shark nets. So I made sure I stayed in the middle of the pack for that one." And, elsewhere in China, there was a dead dog too.
The biggest obstacle of all is the opponents. There are no lanes in the lake, and at times contact is unavoidable. "It certainly has its elements of being competitive," Payne admitted. "You can imagine that there's 25 girls and 25 guys stood on a pontoon and you're all trying to get to the same place. There's always going to be a little bit of friction. But nine times out of 10 it is an accident if someone hits you when someone swims past.
"You have a boat with a referee on it that follows us the whole way round. They have the same system as a football system, so two yellow cards makes a red."
Every advantage counts, then. While Payne triumphed in the World Championships in Rome and Shanghai in 2009 and 2011 respectively, she is excited about the prospect of competing in London this year, and insisted that busy swimmers can still hear the crowd.
"You can hear people cheering for you," Payne said of the atmosphere. "You can't hear specifics, like 'Go Keri-Anne' or anything like that, but you can hear the noise of the crowd. Especially if you're in one of the finals and you're swimming down, all you can hear is noise."
The London water should be well-suited to Payne. "It was brilliant, the water temperature was about 21 degrees, which was very good," she enthused after a morning's training. Last year in Shanghai the water was 30 degrees. "It was really nice to get in there. Being an open water swimmer you have to be versatile, be prepared more than anything. We've always been taught as swimmers to expect the unexpected."
If Payne wins she can expect to be quite a star. She is less famous than her great friend Becky Adlington, who will be a bridesmaid at her wedding this summer, but insists she is happy with this.
If Payne wanted to, she could certainly be a poster girl for British swimming; she was funny and charming yesterday, and might well win gold. But she was clear that media and sponsorship commitments come second to training.
"I'm not running around screaming," Payne added of her modest approach to her achievements.
"Because a lot of people can assume that because you're a world champion the gold medal is already yours, and it's already put round your neck. And I wish it was like that, but it's not, unfortunately. I'm not in the sport to get recognition on the street."