The massive animal has been spotted in the Hudson River at least three times in the last week -- first off the Chelsea and Harlem sections of Manhattan, then to the north in Sleepy Hollow in Westchester County.
"It was gigantic," said Randy Shull, who said he spotted the unusual visitor Sunday afternoon while boating at Kingsland Point Park in Sleepy Hollow. "When we saw it surface, its back was just mammoth."
Last month, trackers saw the manatee as it swam north, first near Delaware, then Maryland, then New Jersey. By Saturday, it was seen in Manhattan.
Kim Durham, rescue program director for the Riverhead Foundation, a nonprofit group devoted to marine mammals, called it a "bona fide" sighting, but there isn't photographic proof.
It is unusual for one of the creatures -- often associated with the warm waters of Florida -- to travel so far north, although they have been reported along the shores of Long Island and even Rhode Island.
Manatees are an endangered marine mammal. Florida wildlife experts counted 3,116 in their annual survey in February.
John Vargo, the publisher of Boating on the Hudson magazine, said his alert about the sightings was met with disbelief by some boaters.
"Some were laughing about it, because it couldn't possibly be true," he said.
"I'm 70 years old, and I've been on the river my entire life," Vargo said. "I've seen dolphins and everything else, but never a manatee."
Copyright 2006 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.