Follow CBSPHILLY Facebook Twitter

ORTLEY BEACH, N.J. (CBS) — A U.S. Army Corps of Engineers beach replenishment project on the Jersey Shore dredged up a mysterious substance that left many beachgoers wondering “what is that?”

Several parents at Ortley Beach kept their children out of the water Thursday as black sludge appeared to be washing ashore.

New Jersey Officials: 47 Beaches Under Advisory After Unsafe Levels Of Fecal Bacteria Detected

“You saw all the brown, black coming down the ocean it was disgusting,” Greg Brutofsky told CBS2’s Vanessa Murdock.

“As soon as you saw the waves come over, it was just black,” Kim Brutofsky, of East Hanover, added. “We just thought it was wood… Horrible, this whole beach was covered.”

“It looked like black coal. But when I went home, my feet were black,” another man added.

Credit: CBS3.

It turns out, the mystery substance is peat. It’s an organic material that might not look pretty but is not harmful to swim among or walk in, Murdock reported.

“The perception is ‘Oh my god, it’s oil or tar or something like that.’ It’s not dangerous, it’s organic, it’s decayed vegetation,” research professor of coastal engineering at Stevens Institute of Technology, Jon Miller explained.

He said the Corps is actually dredging up a bit of history.

“The peat actually forms where there used to be a wetland or a marsh. So the fact that the material is offshore, it just kind of indicates that a long time ago the shoreline was much farther offshore,” he said.

Toms River Township Engineer Robert Chankalian said he initially thought it was coal, too.

SummerFest Heads To The Blueberry Capital Of The World: Hammonton, New Jersey

“We raked it this morning. As you can see, the beach is clean now, and they’re now down into the good sand,” he said.

That came as little consolation to grandmother Judy Muschla, of Jackson.

“I have my granddaughter here. She likes to play in the sand, and I’m reluctant to let her sit in the sand,” she said.