HUNTINGTON BEACH, Calif. (AP) — Federal officials on Tuesday recommended increasing the distance from undersea pipelines that vessels are allowed to anchor in Southern California, citing a 2021 oil spill they said was caused by ships whose anchors were dragged across a pipeline after a storm.

The leak occurred in a ruptured pipeline owned by Houston-based Amplify Energy. National Transportation Safety Board officials concluded damage to the pipeline had been caused months earlier when a cold front brought high winds and seas to the Southern California coast, causing two container vessels that were anchored offshore to drag their anchors across the area where the pipeline was located.

The October 2021 spill of 25,000 gallons (94,600 liters) sent blobs of crude washing ashore in Huntington Beach and nearby communities, shuttered beaches and fisheries, coated birds with oil and threatened area wetlands.

The Beijing and MSC Danit — each measuring more than 1,100 feet (335 meters) long — had displaced and damaged the pipeline in January 2021, while a strike from the Danit’s anchor caused the eventual crude release, officials said.

The NTSB concluded that the pipeline rupture was likely caused by the proximity of anchored shipping vessels. The agency’s board members recommended that authorities increase the safety margin between ships anchored on their way to and from the ports of Los Angeles and Long Beach and undersea pipelines in the area.

They also urged vessel traffic services across the country to provide audible and visual alarms to those tasked with keeping watch when anchored vessels near pipelines. Procedures are also needed to notify pipeline operators when a potential incursion occurs, they said.

The recommendations as well as several others followed a nearly four-hour hearing on the spill, one of the largest in Southern California in recent years.

Andrew Ehlers, the NTSB’s lead investigator, said the pipeline that ferried crude from offshore platforms to the coast was located at a distance of about 1,500 feet (457 meters) from vessel anchorages in the area.

Amplify, which pleaded guilty to a federal charge of negligently discharging crude after the spill, said the pipeline strike was not reported to the company or to U.S. authorities. “Had either international shipping company notified us of this anchor drag event, this event would not have occurred,” the company said in a statement.

Since the spill, Amplify agreed to install new leak-detection technology and also reached a civil settlement with local residents and businesses that provide surf lessons and leisure cruises in Huntington Beach — a city of nearly 200,000 people known as “Surf City USA” — which claimed to have been adversely affected by the spill.

Meanwhile, Amplify and local businesses sued shipping companies associated with the Beijing and Danit. Those suits were settled earlier this year.