On a busy early morning in London, tourists snapped pictures of the sunrise from London Bridge as commuters dodged around them, the hustle and bustle of a city going about its day. But though I stood just meters away, on the foreshore of the River Thames, I might as well have been alone. My eyes were focused on my feet—or, more specifically, the surrounding mud. The banks of the river contain thousands of years of the city's history, and it's easy to see if you know how to look.

Walking along the foreshore, I spotted something that looked promising: a glint of bright orange peeking out from between some rocks, just waiting to be picked up. It was a tiny fragment of decorated Roman pottery called Samian ware—its warm reddish glaze and smooth surface were unmistakable. Nothing could have dampened my excitement when I realized I was likely the first person to hold it in 1800 years.

London is full of mudlarks like me—amateur archaeologists who search rivers for urban artifacts, looking for any old items the waters wash out of the mud. Some lucky mudlarks turn up Stone Age tools, mammoth teeth, bronze swords, medieval rings, and coins by the bucketful. Some of these artifacts can be found at the Museum of London, which is packed with objects rescued from the Thames that would otherwise have been lost.

With each tide, new layers of London’s history are exposed. The Portable Antiquities Scheme, a program headed by the British Museum and Amgueddfa Cymru-National Museum Wales, collects data on historically significant artifacts found by mudlarking, like Roman pottery and coins, Bronze Age bones, medieval spindles, or Elizabethan collar pins. Mudlarks are required to alert the scheme to potentially valuable objects that appear to be more than 300 years old [PDF]—which fall into the legal category of treasure—but in most cases, they get to keep what they find, showing off their amazing items on Instagram and Twitter.

Mudlarking wasn't always such a trendy hobby. In the 18th and 19th centuries, mudlarks were often poor children who foraged the foreshore for anything they could resell, such as nails or lumps of coal. Even congealed fat tossed overboard by a ship’s cook could be sold to an unscrupulous restaurant.

While it’s possible to start mudlarking with a basic trowel or metal detector, rubber boots and gloves, and required permit, extreme mudlarks take the hobby to a new level, using watercraft and technology to unearth history. Nicola White, an avid mudlark, uses kayaks, boats, and hovercraft in her hunt for artifacts, and lets viewers tag along via her YouTube channel.

Mudlark Nicola White holds a pipe she found on the Thames foreshore.Nicola White

Growing up by the beaches of Cornwall, White spent her time scanning the sand for anything interesting that the tide washed up. But she really caught the mudlarking bug after she moved to London in 2000. “I wandered along the Thames path and, as it was low tide, I ventured down the stone steps to the foreshore,” she tells Mental Floss. “Then one day I found a coin. It wasn’t particularly old—it was a George V penny—but I was so excited. It was the idea that someone had dropped that almost 100 years ago, and I was the first to hold it. It really is history you can touch.”

After spending £90 on the permit (which is good for three years), White was all set to look further afield.

According to White, kayaks are the simplest way to get around, but they can turn up big finds. In 2019, a kayaker simply reached down into the shallow water and pulled up Roman glass and pottery from a possible shipwreck. In her kayak, White has been able to explore some spooky places, like the abandoned military forts that dot the Thames estuary. “The forts are now overgrown and, in the case of Darnet, flooded, but they exude an aura of peace and calm and secrets,” she says. “Evidence of the forts’ military past is gradually being obscured by nature.” Ferns, brambles, and ivy now cover the walls. Owls and kestrels make their nests in the old gun casements.

Nicola White found this coin dating from the reign of George II (1727-1760).Nicola White

Some sites on the Thames, like these forts, require special permission to visit. Other sites, such as scheduled monuments, are off-limits. But there are many places that, so long as the inherent dangers are taken into account, anyone can go—if they have a boat or kayak. “It is exciting to be able to reach places that would be otherwise out of reach. It awakes that inner adventurer in me each and every time,” White says.

On her Instagram feed, White displays the incredible variety of items she’s uncovered—from Victorian patent medicine bottles and uniform buttons to Roman coins, gold rings, and human bones. But the treasures she values most tell a meaningful story. “One of my favorite finds remains a brass luggage tag with the name of a WWI soldier on it—Fred Jury, of 72 Woolwich Road,” White says. “He was hit by a grenade, lost several fingers, and then came home to marry his landlady and live the rest of his life in Woolwich.” One of her other finds links directly to Pudding Lane, where the Great Fire of London erupted in 1666.

White once went mudlarking on a hovercraft, a vehicle that floats on a thin cushion of air and is powered by propellers. She was able to skim over the squishy mudflats that would otherwise suck mudlarks down into it—never to be found until a future mudlark stumbled across them. “Going out on a hovercraft has been exhilarating and thrilling. [One time] I had to hang on for dear life. Luckily, I only go out on a hovercraft with people who are qualified to handle them,” White says.

In one of White’s videos of her hovercraft expedition, her companion dug up a mostly intact Roman pot. The chance of unearthing pieces of the past keeps mudlarks like White (and me) going out in the cold and wet to search. “I would be very happy to find a Roman pot full of coins, too,” she says. “Well, we can dream, can’t we?”

But there are some potential mudlarking methods that may be too extreme, even for White. “I’ve always fancied scuba diving, actually,” she says. “It’s hard not to imagine what might be on the mud in the middle of the Thames, out of reach. But some things might be better left to the imagination!”