Searching for Underwater Treasure with Magnet Fishers

Magnet fisher James Kane cradles a shiny, four-pound magnetic disk: a stainless-steel shell housing an alloy of iron, neodymium and boron. He hucks it into a lake in a public park in New York City, then tugs it slowly toward shore with a sturdy synthetic rope. As the powerful magnet bump bump bumps along the bottom, it kicks up a line of bubbles—and then suddenly there’s a heavy drag, as if the lake bed has turned to taffy. The magnet is stuck to something. Filmed by his partner Barbi Agostini, Kane hoists their dripping catch: a thick iron rod called a sash weight, a counterbalance used to open heavy windows a century ago.

Over the next few hours on this October afternoon, Kane and Agostini also pull in a 20-year-old flip phone, a signpost, fishing hooks and lures, pliers, bottle caps, batteries and an iPhone 6. They give the smartphone to a girl who’s nearby with her friends, fishing for bluegills. “If it works, I’m going to be so happy!” she says. Then she sniffs the phone and wrinkles her nose. “It smells.”

To magnet fish is to plumb unseen depths for sunken treasure, but it also means getting acquainted with the stinky, the scummy and the bizarre. Agostini’s magnet once clanked onto the lid of a mason jar, inside which floated a dead tarantula in purple liquid. A particularly exciting catch can bring headlines—or the police. The American zeal for guns has sown firearms below the waterline, and magnet fishers harvest them with regularity. Agostini and Kane have found pistols, shotgun parts, Revolutionary War–era grapeshot and modern ammo clips. The two magnet fishers call the police whenever they find a gun, and they do so often enough that some officers recognize them. Last year Kane pulled an inert hand grenade out of New York City’s East River, summoning the police department’s bomb squad to a posh waterfront block in Queens. But the pair’s most notable catch—and probably the most famous thing ever found by U.S. magnet fishers, which Kane says has earned them a mention in an upcoming volume of Ripley’s Believe It or Not!—was a safe containing stacks of waterlogged cash, pulled from a river this past May.

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The $100 bills were so degraded that Agostini and Kane don’t yet know precisely how much they found, but based on the stacks’ thickness, they estimate the total was $50,000 to $80,000. As soon as they could do so after the catch, they took a Megabus to Washington, D.C., to hand deliver the money to the Mutilated Currency Division at the federal Bureau of Engraving and Printing. There it will be counted and eventually paid out to the pair, though processing might take a few years—Kane says they’re in line behind people who had bills blackened by last year’s deadly wildfires in Hawaii.

Agostini and Kane, both age 40, didn’t get into this pastime expecting to get rich; mostly they wanted something to do outside during the COVID pandemic. Magnet fishing, alongside baking sourdough bread and solving jigsaw puzzles, took off in the early months of 2020. “Magnet fishing was so COVID-friendly. You were forced to distance yourself” even if you bumped into a fellow hobbyist outdoors, says Pittsburgh-based archeologist Ben Demchak, who sells specialized magnets through his company, Kratos Magnetics. Magnet fishers, he explains, need to give each other a wide berth in the field; their powerful lures tend toward mutual attraction.

Social media algorithms boosted the hobby, too. Reddit has a magnet fishing forum with nearly 220,000 members. On YouTube, channels such as Kane and Agostini’s Let’s Get Magnetic emphasize the thrills, editing out hours of dragging and dipping for the moment a precious or peculiar item is yanked out of dark water. But magnet fishers say that what has lasting appeal, and makes up the bulk of their time, is taking trash out of the environment. “It’s a good thing to do. You’re cleaning up the water. It’s an amazing feeling,” says Colt Busch, a magnet fisher in Maine, who recently discovered an antique Coca-Cola bottle, intact but empty, embedded in a clump of metal scraps.

Magnet fishers don’t always get a warm reception. Walking near the lakeside after their latest catch, Kane and Agostini are approached by a member of a nonprofit group that partners with the city to help maintain the park. She tells them magnet fishing isn’t permitted here. She adds that she hasn’t called the police—at least, not this time.

Neodymium’s Mighty Pull

No one would be able to fish with neodymium magnets at all if it weren’t for metallurgist John Croat and engineer Masato Sagawa. In the early 1980s Croat, then at the General Motors Research Laboratories, and Sagawa, then at the Sumitomo Special Metals Corporation, were both searching for alternatives to cobalt and samarium magnets, which are powerful but expensive. Independently and almost simultaneously, Sagawa and Croat identified the same intermetallic compound, which is a substance with a fixed ratio of elements: in this case, two atoms of the rare earth element neodymium to 14 iron atoms to one boron atom. “That didn’t exist yet,” Croat says. “The discovery of that intermetallic compound is the invention.” You can’t trip over a rock with the chemical composition Nd₂Fe₁₄B. Such magnets must be created artificially, through sintering or bonding. In what Croat describes as a “shock,” each happened to announce their discovery at the same conference in Pittsburgh in November 1983. Then they changed the world.

Neodymium magnets weren’t simply more affordable. They were strong enough to enable miniaturized computer hard drives and tinier, mightier electric motors. Wind turbine cores have neodymium magnets to efficiently turn kinetic energy into electricity. They are also key components of headphones and speakers, and they remain the most popular rare-earth magnets sold commercially. “I don’t think they will ever come up with a better magnet,” Croat says.

Neodymium magnets, despite their name, are mostly iron. Such magnets contain regions “where all the electrons are lined up like soldiers on parade, all facing in the same direction,” says Andrea Sella, a professor of chemistry at University College London. In neodymium magnets and other permanent magnets—which don’t require electric currents or other external help to stay magnetic—multiple layers of these aligned electrons stack up. The result can be imagined as a pattern like three-dimensional wallpaper. Sella likens the structure to a series of unending nightmares. “Every time you move a certain distance, oh, my God, you’re back where you started,” he says. The neodymium, even in a relatively tiny amount, helps pin the iron atoms in place in this repetitive crystalline lattice.

“Magnetism is really a reflection at a macroscopic scale of the quantum phenomenon called spin,” Sella says. This property is often described in terms of an atom’s nucleus or its particles spinning about an axis. But that’s a fairly crude mental picture, he says. The reality is that spin “represents something about the fundamental nature of the particle.”

As a quantum phenomenon, magnetism might seem ethereal. But it can quickly become much less so when handling actual neodymium magnets: Agostini says she once found herself stuck to a subway seat, held fast by a magnet in her backpack. If two neodymium magnets get too close, they can slam together, crushing a wayward finger in a painful metallic sandwich. When two of them accidentally bump each other, Kane strains to separate them, like he’s breaking apart the world’s most frustrating KitKat bar.

Stores like Demchak’s sell neodymium magnets according to their shape and pull force, measured in the thousands of pounds. A “360,” for instance, is a solid magnet housed in a metal cylinder. To comply with the regulations for shipping these objects by air, Demchak nests them in boxes of foam to buffer the magnetic fields. Shipping magnets in the U.S. by ground doesn’t have such restrictions, he says, although he now packs those parcels carefully, too. He learned his lesson after selling his first 360—which never made it to the customer. It probably got stuck somewhere in a mail processing plant, he says. Or maybe it’s still out there, clamped to the belly of a delivery truck.

Deep Cleaning?

Once the Bureau of Engraving and Printing sends them the funds from the mutilated cash, Agostini and Kane say they want to use the money toward a down payment to move out of New York City. Agostini would like to buy a place with enough space to raise chickens, dogs and goats. She loves animals, she says, and considers magnet fishing to be an extension of this because it helps clear pollution from their habitat.

“If you really talk to magnet fishers, you can tell they have a sense of pride about it—they’re cleaning up the waterways,” Demchak says. For example, he notes that magnet fishers recently helped pull hundreds of electric scooters out of a river that runs through the campus at Michigan State University. Busch says he has caught more than 140 bicycles since he began magnet fishing. And there’s plenty more trash to collect. “As much as I clean up the water,” Busch says, “I feel like there’s three times as much junk left to pull up.”

If there have been comprehensive scientific reports on the environmental impact of magnet fishing, they aren’t in any mainstream databases. Only a handful of studies even reference the hobby, such as a 2024 analysis in the journal Hydrobiologia of Hungarian magnet fishers’ social media posts that evaluated how much discarded fishing gear had been recovered since 2016. Photographs and videos posted online showed that magnet fishers pulled in more than 2,000 pieces of gear, including rods, reels, hooks and other items, from Hungary’s waterways.

It’s helpful when magnet fishers remove sharp bits of metal, which can be physical hazards to swimmers and wildlife, points out Timothy Hoellein, an aquatic ecologist at Loyola University Chicago, who studies trash in freshwater environments. Electronic devices and batteries also contain heavy metals, such as cadmium and mercury, plus other chemicals that are potentially toxic to “microorganisms, or invertebrates, or fish or people,” he says. Dull iron is not a particular danger to anything, though, he says; soils already contain natural iron and rust.

But lake beds can host things worse than rust. Toxic chemicals such as polychlorinated biphenyls, or PCBs, can stick to charged particles in sediments. Fine silts and clays also retain pollutants such as microplastics and particles from nuclear fallout, as well as nutrients, including nitrogen and phosphorous, which can harm ecosystems if concentrations are too high. Releasing these trapped materials presents a possible downside to magnet fishing. “Any practice that could disturb the sediment at the bottom of a lake, especially an urban or periurban lake, has the potential to resuspend this sediment—and any associated pollutant—back into the water column,” says Phil Owens, an environmental sciences professor at the University of Northern British Columbia. Whether magnet fishing has a “net positive or net negative effect on lakes and ponds” could depend on the individual body of water, its surroundings and the intensity of magnet fishing activity. 

Hoellein hypothesizes that such disturbances are minor relative to magnet fishing’s potential benefits. “There could be some sediments with industrial chemicals or other pollutants that are released back into the water through magnet fishing, but I don’t know if it would be that different than a major storm coming through” and agitating a lake floor, he says.

Plus, magnet fishing dredges up an additional perk: it gets people outdoors, where they can enjoy often-overlooked waterways. A few urban bodies of water are shunned for a good reason, though—the Environmental Protection Agency says New York City’s sludgy Gowanus Canal is one of the most contaminated water bodies in the U.S. (Kane would love to magnet fish there but says he hasn’t because the canal water is “very bad for your health if you get it in your facial area.”) But many other aquatic areas in cities are unfairly dismissed as too dangerous or unpleasant to be around, Hoellein says. Or they’re treated as junkyards. That’s a counterproductive attitude, he says, “especially in places where we also drink from that same water.” He welcomes anyone who wants to contribute, in their own style and with the time they have, to fixing the problem of environmental trash. “For some people, that’s magnet fishing,” Hoellein adds.

Know before You Throw

At the shore, the magnet fishers and the nonprofit staffer reach a détente; the discussion turns to a mutual appreciation for local history. Later, privately, Kane insists he has played by the book: he has a fishing license and a metal-detecting license, and this lake is in a public park.

Magnet fishing is permitted in publicly accessible places in the U.S. But it might also be subject to local rules and regulations. Although magnet fishing is not specifically mentioned by the New York City Department of Parks & Recreation in its publicly listed regulations, “using magnets to retrieve sunken metal objects can have negative impacts on local wildlife and is against [Parks] rules in any bodies of water under Parks jurisdiction,” wrote a spokesperson for the department in an e-mail to Scientific American. The spokesperson added that the applicable rule is Section 1-04(b)(1)(iii), which prohibits disturbing vegetation.

Demchak’s rule of thumb is that “if you could fish with a fishing pole, for the most part, you can magnet fish.” Certain historic sites, however, can be off-limits to magnet fishers. In fact, fearing the destruction of delicate submerged artifacts, South Carolina has outlawed magnet fishing under the state’s Underwater Antiquities Act. It’s the only U.S. state to have made the hobby illegal in public areas.

If you ever decide to toss a magnet into a lake (where legal), Kane and Agostini offer a few pointers: Be up-to-date on your tetanus shots. Bring a first aid kit for scrapes and pokes and a large bucket for the garbage you will inevitably find. Dispose of that junk properly or sell it to a scrapyard. Wear thick, protective gloves and clothes you don’t mind getting muddy. And look out for the click—the haptic sensation that travels up a rope when a magnet has stuck to something hard and hollow, such as a safe. It’ll probably be trash, but then again, you won’t know until you pull it out of the water. “We still get excited,” Agostini says, “because it’s a mystery every time.”