Manatees - large aquatic mammals sometimes called sea-cows - are fleeing the unseasonable cold in Gulf of Mexico for the warm waters of power plant discharge canals.
More than 300 manatees swam into the outflow of Tampa Electric's Big Bend Power Station in Florida on Tuesday.
Manatees cope poorly with cold conditions, which can affect their immune systems and lead to death.
'Cold stress' killed large numbers of the gentle sea creatures in 2010.
The waters of the Tampa Electric plant are "like a warm bathtub for them," Wendy Anastasiou, an environmental specialist who has been watching the mammals loll about there, told the Associated Press agency.
"They're not blubbery mammals. They're very lean," Ms Anastasiou said. "They need a warm place to go."
Another 50 of the animals also gathered in the warm waters of a power station in Broward County, Florida.
Manatees will sometimes move to colder temperatures to find sea grass - a staple of their diet - but many will go without food for days in order to stay in the warm canal.
Unusual weather patterns are wreaking havoc on Florida's manatee population, with recorded deaths from cold stress increasing rapidly in recent years.