Hundreds of Nike trainers have appeared on beaches across the world from the Bahamas to Cornwall and Ireland.
The bizarre haul first started showing up last September on the remote Flores Island of the Azores where a beach cleaner retrieved around 60 unworn shoes.
Initially they were dismissed as lost property but as the numbers soar, experts believe they've come from a single cargo ship incident.
All are the same style and many have the same production dates sewn inside.
"A friend in Ireland asked if I had found any. I went out the next day and found quite a few. Beach cleaners or beach-combers tend to network, so if a certain item is washing up, we quickly find out about it and we're then on the lookout," explained Tracey Williams, a beach cleaner from Cornwall.
"I think it would be good if companies could be more open about cargo spills - if they could put their hands up and say: 'Yes there has been an incident," Tracey continued.
The footwear has also turned up in Bermuda, the Bahamas, France, Orkney and the Channel Islands.
Gui Ribeiro - the Azores beach cleaner - said: "Through the research I have done everything indicates they may have been from some of the 70 to 76 containers that fell overboard from the Maersk Shanghai."
In March 2018, the 1,063ft vessel capable of carrying more than 10,000 shipping containers was travelling from Norfolk, Virginia, down the east coast of the US to Charleston, South Carolina.
On the evening of 3rd March, close to the coast of North Carolina, a stack of its cargo-laden containers toppled overboard during a storm.
However, it has never been confirmed if the trainers were on-board this ship.
Lauren Eyles, from the Marine Conservation Society, said: "Whatever it is - if it is sinking to the bottom or washing up on beaches - it's going to have a detrimental impact to the marine wildlife.
"The shoes will be breaking down to micro-plastics over years, which will have huge impacts on the amazing wildlife we have both in the UK and worldwide."