Officials are investigating after nearly two dozen dead canines washed ashore on a Washington state island, in what one local has compared to “the start of a horror movie”.

The Skagit county sheriff’s office said 21 canines had been found on the shoreline of Guemes Island, about 80 miles north of Seattle, between 26 March and Friday.

Authorities began “actively investigating” where the animals came from, the sheriff’s office said in a press release issued amid a saga that has baffled the island’s 600 residents.

“It’s a creepy mystery out here,” Olivia Cole, the Guemes Island fire chief, told NBC News. “That’s what I keep saying – it’s like the start of a horror movie, honestly.”

Initially, the carcasses of six canines were found washed ashore at an area called Kelly’s Point, the sheriff’s office said, and an additional five were found in the following days.

Another dead canine was found floating near the coast on Tuesday, and reportedly another nine were subsequently more were found over the next four days.

“This whole island is talking, and there are rumors, because we get big tankers that come through here – and we know there are breeders on other islands,” Cole told NBC News. She said the canines appeared to be the same size, and two of them had orange twine wrapped around their necks.

Skagit county investigators said they have conducted necropsies on the bodies but – because of the deteriorated states of the remains – are not yet sure if the animals are dogs, coyotes, foxes or something else.

Cole claimed the creatures had been skinned. But local news channel Kiro 7 reported that investigators are as yet unsure whether the bodies were skinned or just badly decomposed.

“It was like nothing I’d ever seen,” Ellen Fitch, who found some of the carcasses, told the local news outlet KIRO.

Fitch said locals were “making assumptions” about what happened to the canines.

“Or they’re just exaggerating,” Fitch said. “[People are saying]: ‘Oh, I heard they found wolves and foxes and coyotes,’ [or] ‘Oh, I heard there were witches involved.’”

Guemes Island is accessible by ferry from Fidalgo Island, which is home to Mount Erie. It was known as “Dog Island” in the 19th century, owing to the large number of woolly dogs on the island.