HUNTINGTON BEACH, Calif. (NEWSnet/AP) — An oil sheen spotted near the Southern California coast last week was possibly caused by a natural seep from the ocean floor, U.S. Coast Guard officials said Monday.

Authorities detected the 2.5-mile-long sheen early March 1 near Huntington Beach. Crews recovered about 85 gallons of oil from the water and 1,050 pounds of oily waste and tar balls from the shoreline, the Coast Guard said.

Lab tests have failed to definitively identify the oil source, but preliminary analyses determined it was not a refined product like gasoline or diesel, officials said.

Lab results also were inconsistent with archived samples from oil platforms in the area, Coast Guard said. The samples are more characteristic of “freshly produced” oil typical of natural seep, according to officials.

Authorities said initially that were no reports of spills or leaks from oil platforms operating offshore and the sheen did not appear to be growing. That led them to suspect it was a one-time discharge of oil from the ocean floor, a fairly common occurrence.

The Coast Guard said three live birds — a cormorant, a loon and a grebe — were found sullied with oil and are being treated.

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