By noon, public safety and environmental officials said, the local Fire Department had isolated the fuel on the surface of the water and had begun deploying thousands of special pads to soak up the flammable liquid.

Coast Guard officials are searching for the source of diesel fuel that leaked into New Bedford Harbor Thursday morning, coating the nation’s leading fishing port with a red-tinged sheen and spurring a large effort to keep the spill from spreading.

Between 100 and 300 gallons of diesel gathered in several pockets over about a half-mile from the Fish Island Bridge to Pier 3, New Bedford Deputy Fire Chief Paul Coderre Jr said.


Neither he nor other authorities had been able to identify the source of the leak.

“We may not know what caused this,” Coderre said.

The busy port experiences similar spills about five or six times a year, and smaller sheens of fuel coat the surface of the harbor every week, Coderre said.

An apparent diesel spill consisted of red blobs of oil in New Bedford harbor. George Rizer for The Boston Globe/Globe Freelance

“In context for the harbor, this is a minor incident,” Coderre said. “We never shut down the harbor. We’re going on as usual.”

Joining firefighters at the scene were representatives of the US Coast Guard and the state Department of Environmental Protection.

The Coast Guard, which is leading the investigation into the leak, planned to analyze the fuel in an effort to identify the source, said Ed Coletta, a Department of Environmental Protection spokesman. He said the Coast Guard was checking boats and security cameras in the area as part of the investigation.

Coast Guard spokeswoman Petty Officer Myeonghi Clegg said it was unclear whether investigators would find the leak’s source.

Coletta said the leak pales in comparison to what was considered a major spill in 2003, when about 98,000 gallons of oil destined for a nearby power plant leaked from a barge in Buzzards Bay.


Coderre said most of the fuel would be recovered Thursday, but the cleanup would last several days.

“We will probably be chasing some minor areas of buildup,” he said.

New Bedford Harbor last year landed more than 130 million pounds of fish, valued at $306 million, more than any other port in the country, according to the harbormaster’s office.

David Abel can be reached at dabel@globe.com. Follow him on Twitter @davabel. Jasper Craven can be reached at jasper.craven@globe.com or on Twitter @Jasper_Craven