Australian cops discovered there was something fishy about this would-be murder mystery.

A man turned over what he believed to be a loose breast implant to Queensland state police in the city of Maroochydore, and cops took the report seriously — fearing it could be evidence of a drowning or foul play.

But upon closer inspection, the alleged prosthetic implant was nothing more than a jellyfish.

“Officers at Maroochydore Station were all hands on deck when, much to their initial alarm, a concerned citizen attended the counter to report a possible homicide,” according to a police statement.

The cops continued: “Investigations revealed what police suspected … the item was indeed a jellyfish.”