Manatees in the Hudson and in Long Island Sound
They are extremely rare, but they are not unprecedented.
Steve Stanne, of the New York State Hudson River Estuary Program, told me that a young man named Dan Zinder, who is working on the Hudson under the auspices of the Student Conservation Association, found a website that refers to a previous visitor, a manatee dubbed Chessie that in 1995 was tracked north through New York Bay and past the Statue of Liberty (that is, through the Hudson River estuary), through Long Island Sound and as far east and north as Point Judith, in Rhode Island, where it was seen on August 16, 1995.
Here he encountered cooler water and turned around to return to the warmer waters of Long Island Sound. His radio tag broke free on 22 August in New Haven, Connecticut, but public sightings were received as he continued his journey south.