More oil from a massive offshore spill has washed up on the southern California shore, with beaches closed and fish and birds washing up on shore.
Officials are investigating whether a ship's anchor striking a pipeline could have triggered the leak.
Crews dressed in white coveralls and helmets raced on Monday against an approaching storm as they cleaned damage from 3000 barrels of oil that spilled into the Pacific Ocean in recent days from a pipeline connected to an offshore facility owned by a unit of Amplify Energy Corp.
Amplify CEO Martyn Willsher said at a news conference on Monday it was possible a ship's anchor could have struck the pipe line. Earlier, he said the line was shut and its remaining oil removed. The company's shares plunged 44 per cent in heavy trading.
The Coast Guard is assessing whether one of numerous ships anchored off the California coast could be responsible, said Captain Rebecca Ore.
Amplify's Willsher said the company has identified an area that could be the source of the leak, which divers will review. However, Orange County District Attorney Todd Spitzer said Amplify's divers should not go near the pipeline without supervision from independent investigators like the US Coast Guard.
"The company should not be responsible for leading its own investigation with respect to the hundreds of millions of dollars of devastation to our environment and our economy," Spitzer said.
Huntington Beach, about 65km south of Los Angeles, had 34 square kilometres of ocean and portions of its coastline "covered in oil," said Mayor Kim Carr. The town, which advertises itself as Surf City USA, is one of the rare places in Southern California where oil platforms are visible from the beach.
Huntington Beach pier, a popular surf spot, was closed and the water was empty.
Some 23 oil and gas production facilities operate in federal waters off the California coast, according to the US Bureau of Ocean Energy Management. Amplify's Beta Offshore unit has three, including the Elly offshore platform, where the pipeline was connected.
Federal officials have stepped up scrutiny of ageing and idled offshore energy pipelines. Energy companies have built 64,000 km of oil and gas pipelines in federal offshore waters since the 1940s.
Regulators have failed to address risks from idled pipelines, platforms and other infrastructure on the sea floor, the watchdog US Government Accountability Office (GAO) said this year.
"As pipelines age, they are more susceptible to damage from corrosion, mudslides and sea floor erosion," GAO said.