The California oil spill was triggered after a cargo ship travelling in rough seas dragged an underwater pipeline and pulled it across the seafloor, according to media reports citing statements from investigators. The incident happened months before the oil leaked into the ocean.

A team of federal investigators trying to chase down the cause of the spill boarded the Panama-registered MSC DANIT just hours after the massive ship arrived this weekend off the Port of Long Beach, the same area where the leak was discovered in early October.

According to SondraKay Kneen, a member of the United States Coast Guard, the ship’s anchor collided with the 16-inch steel pipe in January while visiting through the area during a heavy storm.

The coast guard official added that the impact from the vessel’s anchor could have damaged the casing of the steel pipe and then pulled it more than 100 feet. The incident reportedly bent the pipe but did not break it, according to reports from Associated Press.

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Still undetermined is whether the impact caused the October leak, or if the line was hit by something else at a later date or failed due to a preexisting problem, Kneen said.

A day before the statements were given, the Coast Guard announced that the owner and operator of the pipeline was a party of interest in the investigation of the spill, which released about 25,000 gallons of crude oil into waters off the coast of California.

The investigation into what caused the spill could lead to criminal charges or civil penalties, but none have been announced yet, and Kneen said the probe could continue for months.  

The impact of the incident was not limited to beach cleanups and closures. According to reports from Associated Press, the spill killed large numbers of birds and fish.

(With AP inputs)