A mysterious black substance has shown up on one beach at the Jersey Shore.

Visitors to Ortley beach said that the substance looks like black rocks and pebbles, but it crumbles easily.

“It looks like we are looking at an oil spill that has coagulated,” said Joe Sanosi.

Matthew Kane said, “We really don’t’ know what it is. We’re thinking it’s tar.”

The substance began washing up on the beach Wednesday, not long after the Army Corps of Engineers started dredging off the coast. It is part of the beach replenishment project.

But now some residents said that they want to know more about the project and what effects, if any, it could have on the environment, wildlife and people.

“Our concerns are for…the effects on human people if they go in [the ocean],” said grandmother Monica Simpson, who was not letting her grandkids swim.

“Yesterday you could see clearly on the bottom how far you were out. Now it’s black,” said Matthew Kane.

Other beachgoers said that the substance is showing up on their bathing suits and skin when they get out of the water.

“We may ask for a refund because this is gross,” said Megan Kane.

The beach remains open, and people are allowed to swim.

News 12 New Jersey attempted to reach the Army Corps and Ortley Beach officials for comment but did not hear back.