The West Indian manatee, a species classified as "threatened" under US wildlife protection laws, was found on Sunday in the headwaters of the Homosassa River on the state's west coast.

A US Fish and Wildlife Service spokeswoman said the manatee did not appear to be seriously injured.

The Citrus County Chronicle published a video showing an underwater view of the slow-moving mammal, with the word "Trump" written in big letters.

It was also not clear if the act was meant to bring attention to President Donald Trump, a Florida resident.

The Tucson, Arizona-based Center for Biological Diversity said it was offering a $US5000 ($A6500) reward for information leading to a conviction in the case.

Harassment of manatees is a federal offence punishable by a fine of up to $US50,000 and/or up to one year in prison.

Manatees, nicknamed "sea cows", are protected under US law.

Strikes by boats are the top cause of death for the mammal; but loss of habitat, algae blooms and disease also threaten them. There are more than 6300 manatees in Florida, up from about 1267 in 1991.

Reuters with AP

Australian Associated Press