It was one funny bone.

Authorities in Washington state fell victim to a Halloween prank after they responded to a call about a human skeleton — only to find it was a skull-shaped beer bong.

A Washington Department of Fish and Wildlife police officer, a Pend Oreille detective and a border patrol agent responded to a report of human remains spotted by paddleboarders inside of a cave on the Pend Oreille River near the Canadian Border last week, according to WDWF.

The WDWF officer and detective entered the cave entrance on jet skis, then jumped in the water and swam to further investigate.

The wildlife officer dove down to get a closer look with a pair of goggles loaned from a local boater only to discover, fortunately, that he had been duped.

The “remains” ended up being nothing more than a plastic skull beer battle that a prankster had stuffed full of rocks to look like a skeleton.

“Little did they know the trick worked, maybe too well,” the department said.