Image source, ReutersImage caption, Beaches have been closed and residents have been told to avoid the shoreline

An oil slick off the coast of California has started washing ashore, killing fish, contaminating wetlands and closing beaches.

About 3,000 barrels of oil have spread over an area covering 13 square miles (33 sq km), off the Orange County coast.

Huntington Beach Mayor Kim Carr said portions of the coastline were covered in oil.

An investigation into the pipeline breach that caused it is under way.

The slick, about five miles off the coasts of Huntington Beach and Newport Beach, was discovered on Saturday morning.

It's thought to be one of the largest oil spills in the state's recent history, according to Associated Press.

Authorities are now attempting to contain the oil by using protective booms. Divers are also working at the scene to determine how the leak occurred.

"Wildlife is dying. It's very sad," Orange County Supervisor Katrina Foley told CBS News. She added that there were reports of dead animals along the shore and Talbert Marsh, an ecological reserve had also suffered "significant damage".

Image source, EPAImage caption, Some 3,000 barrels of oil have spread over an area of the Orange County coast

The US Coast Guard said it had rescued one duck that was covered in oil and is investigating other similar reports.

Amplify Energy Corp, which owns three off-shore platforms, said it stopped operations and shut its pipeline on Saturday.

CEO Martyn Willsher said the pipeline had been suctioned to ensure that no more oil would spill.

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The area, 40 miles south of Los Angeles, is extremely popular with surfers. Beaches have been closed and the last day of the Pacific Airshow was cancelled.

Residents have been told not to approach animals affected by the spill and to instead call authorities.

Image source, ReutersImage caption, The spill is thought to have been caused by a pipeline breach

Michelle Steel, a Republican representative for part of the affected area, has asked President Joe Biden to declare a major disaster, which would allow for funds to help with clean-up operations.

In 2010, the Deep Water Horizon incident off the Gulf of Mexico saw nearly 300,000 tonnes of oil spill, resulting in the death of thousands of species ranging from plankton to dolphins.

There were also other longer-term impacts on marine life including impaired reproduction, reduced growth, lesions and disease.