The US Coast Guard did not investigate initial reports of a major oil spill affecting the California coast for nearly 12 hours because it did not have enough corroborating evidence and was hindered by darkness and a lack of technology.
Rear Admiral Brian Penoyer told the Associated Press the coast guard was alerted on Friday night by a "good Samaritan" that there was a sheen on the water.
It put out a broadcast to the many cargo and tanker ships anchored off the Los Angeles and Long Beach ports seeking more information, but did not receive any supporting reports.
Penoyer said it was common to get reports of a sheen near a busy seaport. It was more than 12 hours after the report before an oil pipeline company reported the incident.
The spill has sent about 570,000 litres of heavy crude into the ocean off Huntington Beach, which washed onto miles of beaches and a protected marshland.
The beaches could remain closed for weeks or longer, a major hit to the local economy. Coastal fisheries in the area are closed to commercial and recreational fishing.
"In hindsight, it seems obvious, but they didn't know that at that time," Penoyer said.
"So putting yourself in the position of what they did know, this is a very normal process."
The source of the leak was a 27km pipeline that was bent and had a large split in it and had been displaced by 32m on the sea floor, Coast Guard Captain Rebecca Ore said at a news conference.
Investigators are looking into whether a ship's anchor may have struck a pipeline on the ocean floor.
Amplify Energy CEO Martyn Willsher said an anchor from a cargo ship striking the pipeline is "one of the distinct possibilities" behind the leak.