An Austrian tourist has become the third victim of a shark attack along Florida's Gulf Coast in under a week.
Despite the spate of recent shark attacks, such incidents are rare
Armin Trojer, 19, of Baden, was bitten in chest-deep waters off Boca Grande, 230km (140 miles) north-west of Miami.
He was airlifted to hospital in Fort Myers for surgery on torn ligaments and tendons, a hospital spokesperson said.
A 16-year-old boy lost his leg in an attack in Cape San Blas on Monday and a girl, 14, was killed 100 kms (60 miles) further north near Destin on Saturday.
Mr Trojer was bitten on the right ankle while he was in waters near the lighthouse at Gasparilla Island beach, officials said.
"It is a confirmed shark attack," said Lee County sheriff's spokeswoman Ileana LiMarzi said.
She said swimmers in the area were being alerted, but the beach had not been closed as no other sharks had been spotted by air surveillance.
Hospital spokeswoman Pat Dolce said Mr Trojer was in a good condition in hospital as he awaited surgery.
The incident happened about 450kms (280 miles) from the shark attack in Cape San Blas on Monday.
Craig Hutto, 16, from Tennessee, was fishing in the waist-deep waters when he was bitten. His leg had to be amputated.
On Saturday in neighbouring Walton County, Jamie Marie Daigle, 14, from Louisiana, was killed as she swam on a boogie board with her friend.
She was about 100 metres (yards) from shore when the shark tore into her leg.
Bull sharks are believed to have been responsible for the first two attacks. It is not yet known what type of shark was involved in Friday's incident.
Shark attacks remain rare, with 55 unprovoked attacks in 2003, according to the International Shark Attack File.