HUNTINGTON BEACH, Calif. (CNS) — An oil sheen has been spotted about two nautical miles off the coast of Huntington Beach, two months after a large oil spill, and officials Thursday were working to determine how large it may be and what was the source.

Huntington Beach police reported it was about 20 yards by 150 yards.

The U.S. Coast Guard received a report about the oil sheen at about 4:30 p.m. Wednesday, said U.S. Coast Guard Petty Officer Aidan Cooney.

"It was getting too dark to send out our assets, so we contacted other agencies nearby to see if they could assist," Cooney said.

Officials from Cal Fire and the state Fish and Wildlife Service sent out aircraft and boats to check out the report, Cooney said.

"They found some sheen, pulled a sample and we're waiting for test results to identify the source," he said.

Orange County Supervisor Katrina Foley said she was informed that there was a "pinhole leak" in a pipeline, but officials said they did not know which one. It is expected to be a minor leak, and at this point the experts believe it is gas that is in the water, she added.

Orange County CEO Frank Kim said he was called Wednesday night about the incident. He directed the county's public works department to help build a berm at Talbert Marsh Wednesday night at the city's request.

Huntington Beach firefighters smelled "a strong petroleum scent" that indicated some kind of oil sheen near the coastline.

Oil response officials were deployed Wednesday night but did not find any evidence of oiling and decided to do an aerial view Thursday morning at first light, Kim said.

When the sheen was located, they collected a sample and are working to identify the source. There has been no shoreline impact so far.

"It's some kind of sheen and we don't know what it is," Kim said.

Crews were ramping up to build berms at Talbert Marsh, Bolsa Chica and the Santa Ana River if necessary, Kim said.

The sighting came on the same day that the company that owns the underwater pipeline that ruptured in October, leaking thousands of gallons of oil, was indicted along with two of its subsidiaries on a federal charge of illegally discharging oil.

Prosecutors said Amplify Energy Corp. and two of its subsidiaries — Beta Operating Co. and San Pedro Bay Pipeline Co. — failed to adequately respond to eight leak alarms during a 13-hour period, then improperly restarted the 17-mile-long pipeline after it had been shut down in response to the alarms.

Amplify Energy issued a statement Wednesday evening insisting its personnel responded quickly to signs of a possible leak, but they believed the "leak detection system alarms" were false.

All told, about 25,000 gallons of oil seeped into the ocean beginning Oct. 1 from the ruptured 16-inch pipeline, which is submerged about 4.7 miles west of Huntington Beach.