Cameron van der Burgh has admitted using an illegal dolphin kick on his way to winning the 100m breaststroke gold medal but is allowed to keep his medal as FINA are unable to sanction him.
With no underwater technology swimming's governing body has no way to investigate the admission five days after the event, meaning that the South African will retain his gold medal.
Van der Burgh won the title in a world record time of 58.46 seconds ahead of Australian Christian Sprenger and Brendan Hansen of the US.
Underwater footage of the start of the race clearly shows Van der Burgh doing more than the one dolphin kick allowed by breaststrokers on starts and turns.
But the South African claimed he was forced to break the rules because illegal kicking was common-place among the swimmers and policing the rule was poor.
"I think every single swimmer does that," Van der Burgh said. "At the point of time before the fly kick was legal, (Kosuke) Kitajima as doing it and the Americans were complaining.
"It's got to the point where if you're not doing it you are falling behind or giving yourself a disadvantage. Everyone is pushing the rules and pushing the boundaries and if you're not doing it you are not trying hard enough.
Van der Burgh admitted he knew the kick was morally wrong but insisted that unless the rule was enforced he, and other swimmers, would continue to employ the tactic.
"I lost my 50m breaststroke (world title) last year because a Brazilian swimmer (Felipe Franca da Silva) did the fly kicks and beat me," he continued.
"I think only if you can bring in underwater footage that's when people will stop doing it. We will have peace of mind to say I don't need to do it because not everyone else is doing it and it's fair.
"Everybody does it — well, if not everybody, 99 per cent of them. If you're not doing it you are falling behind and giving yourself a disadvantage.
"For me, it's not obviously, shall we say, the moral thing to do but I'm not willing to sacrifice my personal performance and four years of hard work for someone else who is willing to do it and get away with it, and has proven to get away with it, as they did last year.
"I'm really for it if they can bring (underwater technology) in. I'm all for it, it will be better for the sport, but like I say, I'm not willing to lose to someone who is doing it, who has done it to me before."