Five human feet — all detached at the ankle and wearing trainers — have come ashore along a 60-mile stretch of the Georgia Strait, a long gulf between the mainland and the eastern side of Vancouver Island. A sixth foot washed ashore last week has now turned out to be a hoax — a decomposed animal paw placed in a trainer.

Police initially suspected the feet — four of which were all right feet — came from plane crash victims but that has now been discounted. An emerging theory is that they were thrown into the water by a mischievous mortuary worker who would have access to corpses.

Detectives have also been investigating whether a serial killer could be to blame but as yet no DNA matches have been found with missing persons.

The hoax foot has done little to dampen speculation about the source of the previous five severed feet. The string of discoveries began in August, when two size 12 right feet were discovered within a week on the shoreline of the Jedediah and Gabriola islands.

Three more finds came at roughly monthly intervals.

Their remarkably similar nature has spawned dozens of competing theories, including Mafia killings, biker gangs, a people-smuggling attempt gone wrong, a boating accident and even the 2004 tsunami.

Four of the five feet belonged to men and the first four were all right feet. None appeared to have been forcibly removed from a body, but that has not stopped some reports from suggesting that a serial-killer with a foot fetish is on the loose.

Experts say that bodies left in salt water for some time will usually break up in the strong ocean currents, with feet and hands often becoming separated. Training shoes will help them to float. However, even without this week's hoax, the spate of discoveries is highly unusual.

Canadian officials, who are treating the investigation as a criminal inquiry, have so far discounted just one potential explanation: a 2005 plane crash in the Georgia Strait, from which four men are still missing. The families of the victims were told that DNA samples from their loved ones did not match any of the genuine human remains.

Earth Sciences Professor Susan Allen believes that all the feet came from a short distance from where they were found. That rubbished suggestions they could have come from the Asian tsunami victims whose bodies were never found.

"Even with seismic activity, there are all sorts of things happening on our sea floor, something has released this, and of course now everyone's looking," she said.

Criminal lawyer and crime author Michael Slade has speculated a serial killer could be at work. In one of his books, a serial killer puts body parts along the shores of the province to taunt police.

He said that there are several questions he has:

Why are only feet being found?

Why are they all clad in runner shoes?

Why are they being found in the same area?

Why have none been found in the US?

"We also have to consider that this could be a serial killer," he said. "Somebody who right now is underneath the radar. That has to be on the table."

More than 20 happy and healthy young men have gone missing in the British Columbia area of Canada but Slade admits that there is no evidence that their lives came to a violent end.

But he adds: "If those men are all athletically healthy, well you've got a tie-in to running shoes right there."

However a theory fast gaining credibility is that a mortuary worker who has access to bodies is playing a game with authorities.

Richard Thomson, a physical oceanographer with the federal Institute of Ocean Sciences on Vancouver Island said it "could be a rather sick hoax by someone with access to cadavers and running shoes."

So far most feet have been found north of the mouth of the Fraser River:

l A right foot in a size 12 Adidas running shoe was found on Jedediah Island

l A right foot in a size 12 Reebok was found on Gabriola Island

l A right foot in a size 10 1/2 running shoe, was found on Valdes Island

l A right foot in a sneaker was found on Westham Island

l A left foot in a shoe was found on Kirkland Island

Police say it could take some time to conclusively solve the case and have appealed for people to be patient.