A concerned man submitted the “bagged and tagged circular object” to officers in Maroochydore, on Queensland’s Sunshine Coast late last week.
He feared it might have indicated a drowning or possibly a murder.
The police station said in a statement that they had soon confirmed the find was not sinister.
“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,” said the statement.
“Investigations revealed what police suspected… the item was indeed a jellyfish.”
Colin Sparkes, from Surf Life Saving Queensland, said the discovery was most likely a blubber jellyfish.
He said the species was commonly found in Queensland waters and its sting was irritating, but not dangerous.
“[The] tentacles have been knocked off by wave action or eaten by fish,” he said of the one handed to police.