Chessie the manatee, who winters in the waters off Florida but has spent much of the past two summers frolicking in and around the waters of the Chesapeake Bay, is heading north again.

The manatee, which first gained fame when he had to be airlifted back to Florida with fall approaching in 1994, was traveling north at about 25 miles per day in mid-June, according to satellite readings from his radio transmitter.

Last year, Chessie's legend grew when he became the first known Florida manatee to swim to New England and back.

He got as far as Point Judith, R.I., on Aug. 16 before turning around and beginning the trek back to Florida.

Manatees cannot survive in water temperatures colder than 65 degrees.

Bob Bonde, a manatee biologist with the federal government's National Biological Service in Gainesville, Fla., said Chessie crossed the Florida-Georgia border on June 12.

At his current pace, the manatee, who is thought to weigh about 1,200 pounds, could reach the mouth of the Chesapeake Bay in July, Bonde said.

Though scientists believe the Florida manatee population has increased the last 10 to 20 years, they remain an endangered species. An aerial survey found 2,639 manatees in their Florida habitat this winter, though the overall population may be a little larger, Bonde said.

At least 155 manatees were killed this winter by an outbreak of algae known as red tide near Fort Meyers, Fla., he said.

Chessie is one of about 18 Florida manatees whose whereabouts are tracked by radio transmitters. The transmitters contain a sensor that bobs up and down as the manatee moves, and Chessie's shows he's moving north, Bonde said.

Scientists are not sure what causes manatees to wander, and Chessie's 2,000-mile jaunt to Point Judith surprised even the experts.

"If you called me two years ago, I'd have said, 'No, there's no way they can make it up to Rhode Island,' " Bonde said. "So we're learning something new every day."