The combination of sunlight and waves helped evaporate and dissolve some of the oil that blackened beaches and covered wildlife in thick goo after a pipeline on shore leaked up to 105,000 gallons Tuesday.
Federal regulators ordered Plains All American Pipeline to drain the pipe that leaked, test the metal in the damaged section of pipe, and complete a series of steps before it can ask to resume pumping oil through the pipe to inland refineries.
"Before restarting operations, we're going to make sure they do things right," said Linda Daugherty of the federal Pipeline and Hazardous Materials Safety Administration.
Investigators with the agency are looking into the cause of the spill and whether there was something Plains should have known about conditions in the underground pipeline and factors that could have contributed to the accident.
The spill is also being investigated by federal, state and local prosecutors for possible violations of state and federal law.
The pipeline safety agency's corrective action order said the 10.6-mile line had recently been inspected, but the results weren't known. Tests of the 2-foot-diameter pipe in 2012 found 41 anomalies mostly due to external corrosion, frequently near welds, the agency said.
The company has said there were no previous problems with the pipe.
Plains said it could take weeks or even months before investigators find what caused the disaster.
There's no estimate to how much damage the spill caused, but a dead dolphin was found in Santa Barbara Harbor and three dead pelicans were recovered.
It's not clear if the dolphin found in the harbour, about 20 miles from the source of the spill, died from exposure to oil, said Veterinarian Michael Ziccardi.
Two sea lions, an elephant seal and six pelicans have been rescued, said Ziccardi, director of the Oiled Wildlife Care Network.
Workers wearing yellow protective suits, rubber gloves and face masks scrubbed pelicans with toothbrushes in a soapy bath at the International Bird Rescue in the San Pedro section of Los Angeles.
The disaster, which led officials to close Refugio and El Capitan state beaches just before Memorial Day weekend, was sure to make more campers unhappy as the state announced the popular parks and campgrounds would be closed until June 4, longer than originally announced.
Rough seas have made recovery efforts more difficult, and the light sheen of oil was becoming harder to skim off the surface, said Rick McMichael, a Plains representative.
Plains All American and its subsidiaries operate 17,800 miles of crude oil and natural gas pipelines across the country, according to federal regulators.
Since 2006, four subsidiaries of Plains All American have reported at least 223 accidents along their lines and been subject to 25 enforcement actions by federal regulators.
The accidents resulted in a combined 864,300 gallons of hazardous liquids spilled and damages topping $32 million. Corrosion was determined to be the cause in more than 70 of those accidents. Failures in materials, welds and other equipment were cited more than 80 times.
The company has defended its record, saying accidental releases have decreased as the number of miles of pipelines has increased. It said it spent more than $1.3 billion since 2007 on maintenance, repair and enhancement of its equipment.
Associated Press writers Christopher Weber in Los Angeles and Matthew Brown in Billings, Montana, contributed to this report.Suggest a correction