More than 80,000 gallons of a sticky, thick oil spilled into a tributary of the Potomac River last weekend after a pipeline ruptured at Steuart Petroleum distributors in Southern Maryland.
Coast Guard officials said the oil, used to manufacture asphalt roofing shingles and other products, fouled about 400 yards of shoreline along Piney Point Creek in St. Mary's County.
It congealed into a buoyant goo that the company is now scooping from the creek's surface.
Because the material was solidified by the water's cool temparature, state and federal officials said they expect environmental damage to be minimal.
Two foxes were trapped in the sludge and died of shock, but the spill is not likely to cause lasting harm to the waterway, said John Goheen, a spokesman for the state Department of the Environment. None of the material reached the Potomac.
"It is like a big piece of somewhat soft taffy, sitting there on the water," Goheen said. "We are fortunate because it is a solid and it is basically containing itself."
Thinner forms of oil would have spread more quickly and remained in a form that fish, oysters and other wildlife could ingest, he said.
Officials at the company could not be reached for comment.
Goheen said state investigators are looking into the incident, but added that fines are unlikely because it appeared to be an accident and company officials responded quickly in organizing emergency measures and a cleanup.
According to Don Morrow, a senior chief petty officer with the Coast Guard's Marine Safety Office in Baltimore, the company already has removed about 50,000 gallons of the substance using shovels, rakes and backhoes.
The cleanup should be complete within three weeks. Concern about oil spills on the Chesapeake Bay and its waters increased last year after the Exxon Valdez disaster in Alaska's Prince William Sound.
Laws passed last year focused mostly on shipping, increasing the penalties for leaks and requiring oil tankers to carry more cleanup equipment on board.