The Coast Guard and California Department of Fish and Wildlife Office of Spill Prevention and Response are responding to a report of an oil sheen approximately a half-mile offshore near Bolsa Chica State Beach.
The sheen was reported to be 90-by-90 feet.
The source has not been determined.
"All we know is that we've got oil in the water at this point," said Huntington Beach City Councilman Dan Kalmick.
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It is in the same area as a leak from an off-shore oil pipeline in October. A grand jury indicted a Texas company on Wednesday in connection with the spill off Huntington Beach.
A sand berm was constructed Wednesday night to protect the shoreline if the oil moves ashore. Booms also were placed in the water to contain any oil that nears the coast.