Federal and state authorities were investigating an unspecified threat to the water supply in Orlando, home to Walt Disney World , and alerted the public Sunday as a precaution.
Officials characterized the threat as vague and unsubstantiated, but said it was being taken seriously.
Orlando, also home to Universal Studios Orlando, is a destination for as many as 50 million tourists a year, and since Sept. 11 Florida officials have worried that the city's international profile might invite an attack.
"People know (Orlando), no matter what country you go to around the world," said Joyce Dowley, spokeswoman for the Florida Department of Law Enforcement. She added: "I want to stress there is nothing specific about the threat.
Officials said the FBI alerted local and state law enforcement agencies Sunday, and water treatment facilities throughout Orlando and Orange County were locked down and under guard.
A spokesman for Orlando Regional Utilities said the water supply had been tested Sunday and revealed no evidence of tampering.