A large oil spill off the southern California coast was described as an "environmental catastrophe" by the mayor of Huntington Beach on Sunday, as the breach of an oil rig pipeline left dead fish and birds strewn on the sand and offshore wetlands clogged with oil.

An estimated 126,000 gallons, or 3,000 barrels, had spread into an oil slick covering about 13 square miles of the Pacific Ocean since it was first reported on Saturday morning.

The beachside city, about 40 miles south of Los Angeles, was bearing the brunt of the spill.

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

The oil rig was operated by Beta Offshore, a California subsidiary of Houston-based Amplify Energy Corporation. Calls to Beta and Amplify went unanswered.

Officials said they were investigating the cause of the spill and the type of oil involved.