Charter fishing captains and others along the south Mississippi coast say a mysterious black dust has circulated in the air and water near the Gulfport Harbor.

The Mississippi Department of Environmental Quality is investigating, The Sun Herald reported.

“Everybody started talking about it. Everybody thought it was something different,” said Brian Ware, captain of Fish Assassin Saltwater Charters.

Some worry it could be harmful, though they don’t know for certain what it is. Boats have been covered in a fine black dust, staining the sides of their vessels, the newspaper reported. The particles have also drifted onto the water in the harbor.

“Within 30 minutes, your whole boat is covered in it, you’re covered in it,” Ware said. He’s had to scrub the dust off his boat with bleach.

The harbor is home to several charter fishing businesses. Many of them moved there after Hurricane Zeta in 2020 displaced them from the harbor in Long Beach. The black dust has the potential to affect their tours, said Bill Hancock, captain of Reel Outlaw Charters.

“It’s so fine, it has the consistency of talcum powder, so it finds every little crack and crevice,” Hancock said. He’s had to pressure-wash his boat to remove the stains. It also gets in his clothes and shoes.

The cruise company Ship Island Excursions also docks at the Port of Gulfport. Company spokesperson Ronnie Wentzell says he’s seen the dust on boats, comparing it to when a vehicle gets dirty when driving down a dirt road.

Ware, who also works as a helicopter mechanic for the National Guard, is concerned about the effect the dust could have on his business — his customers “don’t want to breathe it,” he said.