POMPANO BEACH, Fla. -

Federal officials say they're investigating reports of swimmers harassing a sperm whale that drifted close to shore as it was dying off a South Florida beach.

Blair Mase of the National Oceanic and Atmospheric Administration tells WTVJ in Miami that the whale was likely ill or injured as it floated Sunday off Pompano Beach.

A bystander told authorities that she saw two swimmers approach the whale twice. She also snapped pictures of one swimmer getting on the whale. She said the whale appeared to still be alive at the time because its tail was flapping in the water.

Mase says the swimmers could have caused more harm and stress to the whale, which later died.

It's a federal offense to harass a marine mammal. Sperm whales also are an endangered species.