Authorities say they're "protecting the integrity and the archaeology of the foreshore".
ADVERTISEMENTThe Port of London Authority has stopped issuing new permits for 'mudlarking' along the River Thames, after experiencing a huge surge in popularity.
The hobby involves searching for historical artefacts washed up along the banks of London's famous waterway.
Any unearthed treasures are supposed to be reported to the Museum of London. But in reality, many historical items are kept by the finder.
"We've gone from about 200 foreshore permits issued four or five years ago, to 5,000 now, and that's a vast increase", said James Trimmer, Director of Planning & Development of the Port of London Authority.
"What we're doing is protecting the integrity and the archaeology of the foreshore", he explained.
Centuries ago, Londoners would have been scavenging for something to sell, but nowadays, the popular pastime is seen as more of a treasure hunt into the past.
Watch the video in the video player above to find out more.