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.
Get San Diego local news, weather forecasts, sports and lifestyle stories to your inbox. Sign up for NBC San Diego newsletters.
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.