Tunisia's Oussama Mellouli won the gold medal in the men's swimming marathon to become the first competitor ever to get medals in the pool and open water.
Britain's Daniel Fogg finished fifth in the 10km open-water competition with a time of 1hr 50min 37.3sec. Mellouli won the 1500 metres freestyle gold at the 2008 Beijing Olympics and used his superior speed to burst clear of his rivals and win the gruelling race in the Serpentine in Hyde Park.
"I can't explain it, I can't really describe it," Mellouli said after pumping his chest when he finished. "I don't think this has ever been done before. This is probably one of the toughest things to do. I'm a pretty solid guy and I never react but you saw that reaction, that says it all."
Germany's Thomas Lurz won the silver medal and Richard Weinberger of Canada the bronze but no one could keep up with 28-year-old Mellouli after he charged into the lead on the fifth of the six loops.
He quickly opened up a three-body-length lead over the chasing pack and maintained his advantage to the end, slapping the overhead touch pads to win gold in 1hr 49min 55.1sec.
"I've been struggling, with my shoulder, my elbow, I had a virus. What happened today is a miracle if you believe in miracles," Mellouli said.