It was a windy night in January, with temperatures in the mid-30s in the Fells Point neighborhood of Baltimore City. But despite the cold, about a dozen people were bundled up and standing on a pier with ropes and magnets in hand.

It was time to magnet fish.

The concept is simple: Tie a high-powered magnet to a rope and chuck it into the water, then slowly pull it back and see what kinds of metal objects come up.

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The headline on this story was updated to say people have been fishing metal out of the Patapsco River with magnets.