Competitors in the 10km open water race are used to dodging sharks and jellyfish. So for Keri-Anne Payne, six laps of the Serpentine will seem relatively sedate.
The open water swim is a bit like the Tour de France. You try to get directly behind someone's feet, or next to their hip, and get swept along in their slipstream, using less energy yourself.
Payne, 24, won silver in this event in Beijing, but is tipped for gold this year after becoming the first athlete to qualify for Team GB, by winning her second world title — in the searing heat of Shanghai, last year. “I had to swim past dead dogs,” she tells RT. “You need to get your head around it, but it is horrible.”
While Hyde Park’s only peril will come from agitated cormorants, there is another danger. The effect of 25 swimmers in such close proximity is a frothing mass of elbows and ankles that’s led to the sport being dubbed “underwater boxing”. Black eyes, broken noses and cracked ribs are an occupational hazard.
The women's 10km begins today at 12 Noon on BBC1, BBC Olympics 9
Keri-Anne Payne - "You have to be hard in Open Water Swimming"