It remains unclear what caused the death of a sperm whale that had been languishing for days off eastern Florida, but a swimmer who climbed atop the 30-foot mammal for what appears to have been an illegal joy ride did not help.

Pompano Beach resident Margie Casey, 49, told NBC 6 that two swimmers approached the whale Sunday morning, and one of them climbed onto the cetacean.

Casey snapped photos from her fifth-floor balcony and sent them to the news station. She said the whale had been alive at the time but seemed to have been on its “last leg.”

The female sperm whale died soon afterward and the carcass washed ashore on nearby Deerfield Beach.

Since harassing whales is a violation of the Marine Mammal Protection Act, the National Atmospheric and Oceanic Administration has launched an investigation of the incident.

“This type of harassment could have caused more harm and added stress to an already stressed whale and ultimately caused its demise,” said Blair Mase, regional stranding coordinator for NOAA. “People need to be aware that they shouldn’t do that.”

Cetacean experts will attempt to determine whether the whale had been sick or injured.

By mid-morning it had drifted to within only 40 feet from shore, and an exhaustive rescue effort ensued.

“I think it’s totally amazing man,” said beachgoer Brad Schwab. “It looks like they’re trying to keep him out in the open sea.”