GRAND RAPIDS, Mich. (WOOD) — A magnet fisherman pulled a World War I mortar from the Grand River in Grand Rapids Tuesday.

The Grand Rapids Police Department confirmed it was a German Granatenwerfer. Police said it would be safely stored until they could safely detonate it using C-4.

Sgt. John Wittkowski told News 8 the department was being “extra cautious,” saying that because the device was so old and had been submerged so long that it was likely no longer very dangerous.

Joseph Alexander said he found the device while magnet fishing near the Sixth Street Bridge.

“I felt something click on. There was something stuck in the mud,” he told News 8.

He managed to get it out of the water.

“I thought it looked like a grenade, but not one I’ve seen before,” he said. “We brought it back home, took some pictures of it, posted it online, and we started getting comments that ‘it’s a grenade, call the police.’ So that’s what we did.”

He said an officer soon arrived and confirmed it was an explosive.

“‘I have to call the bomb squad,'” he said the officer told him. “They sent over an undercover vehicle and confirmed it was live, full, and they boxed it up, put it in a yellow bag, put it in the truck and took it out to what they called the field to detonate.”

Alexander called it his “first cool find so far” while magnet fishing, which he only took up as a hobby about a month ago. He had found knives before.

“I didn’t think anyone would throw a live grenade in the river,” he said. “And for a second there, I was questioning if I was even right.”

He was curious how it ended up in the river. He said the police told him that someone may have brought it back to the U.S., realized it was illegal to have and then got rid of it.