U.S. Coast Guard Capt. Michael McAllister, commanding officer of Coast Guard Sector Charleston, said the source of the spill was unknown after mariners reported seeing tarry, black clumps of oil Tuesday along area beaches, the Charleston Post and Courier reported.
McAllister told the newspaper a Coast Guard helicopter flew over the harbor and saw several oil slicks.
South Carolina Department of Health and Environmental Control spokesman Adam Myrick said a shoreline assessment was to be performed Wednesday to determine the spill's impact on shellfish. He reportedly indicated the department might close shellfish harvesting if the damage is significant.
Charleston residents also reported the spill. Jogger Hannah Dodson told the Post and Courier she was running on the beach near Sullivan's Island when she noticed hundreds of black balls of a gooey substance that smelled of petroleum.