It's a growing problem -- literally and figuratively -- at beaches up and down the Jersey Shore: people digging giant holes in the sand, then leaving without filling them in.

Beach patrols are warning beachgoers against digging holes and not filling them back in at the Jersey Shore. (Getty Images, ThinkStock)

"It's a hazard not only during the day, as well as at night for beachgoers walking on the beach at night, it's a hazard for our mobile units, our ATV's our trucks," said Capt. Randy Townsendof the Harvey Cedars Beach Patrol. "When people don't fill their holes in at the end of the day, it's very easy for someone to get trapped in a hole."

Townsend said what's even more dangerous is digging a deep hole and then trying to dig out a sand tunnel.

"When they dig down deep enough to get their head encaved in sand, and then the sand collapses or caves in on top of them, the more they struggle the harder it is to get out. They're just as dangerous as it is to drown in shallow water," Townsend said.

So who's digging these holes? Apparently many of them are dug by teens who are simply goofing around, Townsend said.

"They do it for funny photos," he said. "I've seen them lay a tarp inside the hole for a tug of war and fill it with water. We want our beachgoers to enjoy the sun and the surf, not dig giant holes that can be very dangerous."

He added the beach patrol is now asking everyone to follow one very simple rule.

"For digging holes on the beach, no deeper than the knees on the smallest person in the group," he said.

According to Townsend, this is a problem on beaches up and down the shore, and "if you see somebody digging a hole let the lifeguard at the nearest tower know, this way we can properly inform those people."

He said in extreme cases, digging a giant hole in the sand can be as dangerous as a shark attack or being struck by lightning. Several large holes, some as deep as 6 feet, have been found in Harvey Cedars in recent weeks.

In 2012, a 12-year-old boy suffocated in Long Branch after a sand tunnel he was in collapsed.