A federal investigation has been launched after a sperm whale was found dead, shortly after it was seen being ridden by at least one unidentified swimmer.

The sperm whale is an endangered species, and experts believe the distressed whale’s death may in part be attributed to the interaction with the reckless swimmer who rode its back.

Witnesses say the whale was described as still alive when it was first photographed with at least one swimmer repeatedly climbing on top of its back, but it may have already been dying by then.

“This whale was likely ill or injured and that is why it came in so close to shore,” Blair Mase, the National Oceanic and Atmospheric Administration’s southeast regional stranding coordinator told NBC Miami.

The animal’s exact cause of death is not known, but wildlife officials say they are not defending the swimmer’s involvement. 

It is a federal offense to harass a marine mammal.

“This type of harassment could have caused more harm and added stress to an already stressed whale and ultimately caused its demise,” Mase said. 

Witnesses say the whale, described at times as having waved its fin out of the water, was somehow fighting the rip current pulling it out to sea while edging closer to shore.

“There’s really very little you can do for a whale if he gets seriously ill or injured,” said Dr. Stefan Harzen of the Taras Oceanographic Foundation.

James Gilbert | Elite.