HUNTINGTON BEACH (California) – Federal investigators and state officials were investigating Monday what led to 126,000 barrels of oil leaking into the Pacific Ocean near the southern California coast.

Huntington Beach is located about 40 miles (65km) south of Los Angeles. It was hardest hit with 13 square miles (33.4 km) of sea and parts of its coastline being “covered in oil,” Mayor Kim Carr said.

Oil appeared to have come from Beta Offshore’s production platform, which is a California affiliate of Houston-based offshore crude oils producer. Amplify Energy Corporation (NYSE:) Amplify didn’t immediately return Monday’s call for information.

Offshore energy pipelines that are aging or inactive have been under increased scrutiny by federal officials. Since the 1940s, energy companies have constructed 40,000 mile (64,000 km) worth of pipelines oil- and gas in federal offshore waters.

U.S. Government Accountability Office stated that the risk from platforms, idled pipelines, and other infrastructure at the seafloor has not been addressed by regulators.

GAO stated that pipelines become more vulnerable to corrosion, mudslides, and seafloor erosion as they age.

Martyn Willsher is an Amplify executive who stated on Sunday that the pipeline carrying oil from this platform had been turned off and any remaining oil filtered out. He said that divers were working to find out the cause and location of the oil spillage.

Officials placed protective booms at 2,050ft (625m) to contain oil and reduce its flow. On Sunday, about 3150 gallons (14,532 liters) were found, according to the U.S. Coast Guard.