Southern California beaches, marshland under threat after massive oil spill

A large oil spill off the Southern California coast left fish dead, birds mired in petroleum and wetlands contaminated, in what local officials called an environmental catastrophe.

The U.S. Coast Guard, heading a cleanup response involving federal, state and city agencies, on Sunday announced an around-the-clock investigation into how the spill occurred.

An estimated 572,800 litres, or 3,000 barrels, had spread into an oil slick covering about 20 square kilometres of the Pacific Ocean since it was first reported on Saturday morning, Kim Carr, the mayor of Huntington Beach, told a news conference.

"We are in the midst of a potential ecological disaster," said Carr, whose beachside city is located about 65 km south of Los Angeles.

Carr went on: "Our wetlands are being degraded and portions of our coastline are now covered in oil."

WATCH | Nearby marshland, home to dozens of bird species, affected:

The spill was caused by a breach connected to the Elly oil rig and stretched from the Huntington Beach Pier down to Newport Beach, an area popular with surfers and sunbathers.