London – Jessica Roux of South Africa dropped out of the women's 10-kilometre open water swim on the fourth of six laps.
She had fallen well off the pace in the gruelling race at the Serpentine, a lake in Hyde Park.
Roux was hoisted onto a safety raft and taken back to shore. She was then carted off in a wheelchair.
Earlier, Fang Yanqiao of China withdrew because of an injury sustained before the race. A release announcing Fang's pullout did not give details of her injury.
Twenty-three swimmers are now competing in the race, which first became an Olympic event four years ago in Beijing. – Sapa-AP