The British Columbia Coroners Service has asked the public to help identify a foot found in West Vancouver, on the shores of the Salish Sea. It might sound like a gruesome find at first,  but it's actually a surprisingly common occurrence in these parts.

Detached human feet in various states of decay have been appearing along the coast of the Salish Sea in southwest British Columbia since 2007 - most of them inside either hiking or running shoes, and usually found by civilians.

Another human foot, found inside a hiking boot, washed ashore on Gabriola Island in May last year. This latest find - from September - was clad in a running shoe. Since 2007, this has become the 20th such find in these waters.

Of the 20 disembodied feet to date, 15 have appeared in British Columbia, and the remaining 5 washed ashore in the US state of Washington, on the other side of the Salish Sea.

But, although the phenomenon is a gruesome one, authorities aren't too concerned about a mad, foot-lopping serial mutilator on the loose, partially because none of the feet show any signs of trauma or of having been forcibly removed.

So how are the feet getting washed ashore, but no other parts of the body? And why - advanced decomposition aside - are they still intact?

It's probably the shoes themselves, experts believe.

"Feet easily disarticulate and when they are attached to a flotation device such as a running shoe, they are easily washed ashore," Gail Anderson, a forensics expert at Simon Fraser University in British Columbia, told Vox in 2017.

"Notice there are no feet washing ashore in stiletto heels or flip flops. Also today's running shoes are much more buoyant than in the past."

In addition, the shoe (and sometimes sock) protects the foot from hungry marine creatures; and it's not uncommon for the feet to saponify, wherein the fatty tissue turns into a solid, soapy, wax-like substance called adipocere.

However, while it's unlikely foul play was involved, the circumstances that lead to a foot making its way to the shore of the Salish Sea are always unpleasant ones.

And identification of the remains isn't easy. Sometimes the feet are greatly decayed. It can also be difficult to match a foot to a missing person based on the information provided to police, and DNA can be too degraded by the salt water for a viable sample to test.

Still, authorities have made good headway in solving these mysteries, having identified 10 out of the 15 feet found in British Columbia - most appear to have involved either suicide or accidental deaths. For now, the latest find remains a mystery.

A version of this article was first published in May 2018.