NEW YORK (CBSNewYork) – People in Brooklyn say treasure hunters are destroying the pristine greens of a popular park.

Some told CBS2’s Ali Bauman it’s become dangerous to walk through Prospect Park and the city is allowing the destruction.

“I almost broke my neck in one of them,” one man said.

“They are kind of dangerous. I trip over them sometimes,” said Bari Johnson.

Jeremy Phillips had no idea why the mysterious pits kept multiplying week after week, until one day he saw people carrying metal detectors and shovels.

All you need is a photo ID to get a free metal detecting permit issued by the Department of Parks and Recreation, which grants permission to dig in more than 100 city parks. More than 500 permits were issued citywide last year.

“I come out here for nature, so it kind of takes away from that,” Johnson said.

The parks department requires that if you dig a hole, you have to restore it to its original condition. As Bauman reported, the problem is: that’s hard to do, and it isn’t happening.

“A lackadaisical approach to filling it back in,” said Phillips. “So even if they fill it, there’s a hole that results.”

“I’ve seen people at night — especially if you come here at night, and you fall, you could hurt yourself,” another man said.

Violators could pay up to a $75 penalty for using a metal detector without a permit. But zero summonses have been issued over the last three years.

The parks department told CBS2 metal detectors are not allowed on athletic fields, flower beds or manicured lawns, but park patrols will heighten their focus on unpermitted use.