Nike trainers have been washing up on beaches across the UK in their hundreds for more than a year after a shipping container lost its cargo in a heavy storm.
Beachcombers in Cornwall started finding the shoes after they began appearing on beaches across the world, from Bermuda and the Bahamas to Ireland and Orkney.
The unworn footwear was first spotted being washed up on Flores Island, in the remote Atlantic archipelago of the Azores last September.
Their numbers became so great that it was clear they were part of something greater than the usual flotsam of abandoned items.
Aside from the vast number, many of the trainers and flip flops appeared to be unworn and many were identical, with the same production dates printed on their labels.
Then, 1,400 miles away in Cornwall, Tracey Williams began to notice a similar trend.
“A friend in Ireland asked me if I had found any,” Ms Williams told the BBC.
“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.”
Many are convinced that the shoes formed part of the shipment being carried by cargo ship the Maersk Shanghai last March.
The Liberian-registered ship had departed from Norfolk, Virginia and was headed down the east coast to Charleston, South Carolina, when it was hit by a storm.
The high winds and heavy seas swept around 70 containers off the ship, the vast majority of which were never recovered.
Two footwear brands, Triangle and Great Wolf Lodge, are said to have confirmed that some of their products that had been on the ship had been retrieved.
Liam McNamara, from Co Clare on the west coast of Ireland, said he had found more than 100 shoes, mostly Nike trainers, and is convinced they came from that vessel.
“One company has admitted to losing stock from that shipment and another admitted losing stock at sea,” he said.
“They’ve been turning up all over the place.”
Dr Curtis Ebbesmeyer, an oceanographer, said the shape of the shoes dictated where they end up.
“The left and the right sneakers float with different orientation to the wind,” he said. “So when the wind blows on them they will go to different places. So on some beaches you tend to get the left sneakers and on others you get the right.”
The World Shipping Council estimates that of the 218 million containers transported annually, more than 1,000 go overboard but experts believe the real number is likely to be higher.
The Marine Conservation Society said products such as trainers harm marine environments but do not count as “harmful” for the purpose of reporting cargo lost at sea.
But it warned that the shoes would break down to micro-plastics over years, which will have a devastating impact on wildlife.