Long before next week's fishing opener, a few Minnesota anglers were avidly casting lines into the water and hauling in hefty catches.

But they weren't hooking walleye, bass or northern pike. They were hoping to reel in an antique metal sign, a safe full of money, maybe even a gun.

It's part of a new, and admittedly niche, sport of magnet fishing, where you "fish" with a super-powerful magnet tied to a strong line.

Most of the time, magnet fishers pull in mundane scrap metal: old nails and bolts, a length of rebar, fish hooks, beer bottle caps. But every once in a while, they might get a bite that turns out to be a submerged bike, an abandoned shopping cart or a Lime scooter that went for a swim.

Websites and breathless YouTube videos are full of memorable metallic fish stories like the 6-year-old who found a stolen safe in the bottom of a South Carolina lake, the Czech magnet fisher pulling a World War II-era German submachine gun from the water or the magnet fisher from Great Britain who found a handcuffed body in a Southhampton river.

Nothing quite that exciting has happened to local magnet fishers, although Marc Hirsh, of Monticello, Minn., once pulled up a picnic table in addition to the more common pocket knives, antique hand-forged nails and railroad spikes.

Scott Thiry, a magnet fisher from Hopkins, has reeled in a bicycle, a specialized tool called a spud wrench and all the fishing hooks he could ever use.

Phillip Marbut Jr., of Waite Park, said his coolest finds are a Zippo lighter, an old metal toy truck and, for some reason, several butter knives. "I don't catch spoons. I don't catch forks," he said.

No magnet fisher can count on getting rich, finding a historical artifact or solving a crime by tossing a magnet into the water. But it's sort of like playing a lucky dip game. You never really know what's lying on the bottom, and what you might pull up when you reel in the line.

"That's the fun of it," said Steven Shoemaker of Elk River, Minn., who also hunts for treasure by panning for gold and using a metal detector. "It's just amazing what people throw into the water."

Part of the appeal is trying to identify what you just hauled up. (A car part? Part of a railroad bridge? A metal shoe for an ox?) And then trying to figure out how it got in the water. (Dropped by a butterfingered boater? Dumped by a litterer? Picked up and put down by a tornado?)

"You always think of people who lose their stuff when they're fishing," Marbut said. "It kind of gets your imagination going."

One magnet fishing website claims that people have used the hobby to find coins, cannonballs and motorcycles under water. The site suggests magnet fishing off piers in harbors because "you could find large metal boxes of cash that may have fallen off some boats."

Even if it's just scrap metal, local magnet fishers don't catch and release, but rather dispose or recycle their finds and consider themselves to be helping the environment by hauling hundreds of pounds of metal out of local rivers and lakes.

"I always bag up everything I catch," said Marbut.

An accidental beginning

Metal fishing is believed to have started in Great Britain when traditional anglers used magnets to retrieve keys or tools they accidentally dropped in the water, according to Michael Taylor, owner of Muscular Magnetics, a two-year-old magnet fishing gear company based in Idaho.

"It's only been in the past four or five years that it's become a thing," Taylor said.

He estimates that there are a few thousand magnet fishers in the United States, although "it's getting out there more and more."

The hobby is also growing in parts of Europe, where there's a lot of metal in canals and other bodies of water thanks to centuries of warfare.

"England is very, very big for magnet fishing," Shoemaker said.

A retired Army helicopter pilot, Shoemaker started the Magnet Fishing Minnesota Facebook group about two years ago. It currently has about 450 members.

As hobbies go, it's a relatively cheap one to get into. Magnet fishing kits sell on Amazon (which include a magnet, line and protective gloves) for as little as $25.99. Muscular Magnetics sells a family kit for $139.99.

The magnets, which are shaped like a hockey puck, are made with neodymium, a rare-earth element that can be used to make high-powered magnets that, in ideal conditions, can grip objects weighing hundreds of pounds.

Besides good heavy gloves, magnet fishing websites also suggest getting a tetanus shot and packing hand sanitizer.

And if you find a gun — "the trophy muskie of magnet fishing," according to Shoemaker — the police should be notified immediately, said Sgt. Natalie Davis, a spokeswoman for the St. Paul police. Anything that might fire or explode shouldn't be handled at all, she added.

Laws of attraction

The activity is so new that it has few regulations.

"Most of the time you can magnet fish anywhere," said Taylor.

However, it's not allowed in state parks, where it's considered a form of metal detecting, which is prohibited, said Ed Quinn, a natural resource program supervisor with the state Department of Natural Resources. State regulations also prohibit the removal of any state property in a state park, with the exception of edible fruit and mushrooms for personal, noncommercial use.

And while local magnet fishers say they often get strange looks, they haven't been prohibited from practicing their hobby.

"I've never had any issue anywhere I've thrown," Marbut said. "We're just pulling rusty old steel out of the water."

Shoemaker uses satellite images and map databases to research historic bridge sites or other places where stuff might have been tossed in the past.

"Places where people drive, a lot of stuff gets thrown over," Marbut said.

But places where there's little traffic, where you wouldn't be spotted throwing something in the water, are also good spots for magnet fishing, Shoemaker said.

"If there's graffiti in the area, that's usually a good sign that someone's dumping stuff," Thiry said.

Despite the abundance of lakes and rivers, there's one problem with magnet fishing in the state.

"Minnesota is pretty doggone clean," said Shoemaker. "You don't see a lot of garbage in Minnesota streams," he said. "It's bad for magnet fishing, but good for the environment."

Richard Chin • 612-673-1775