A 'sardine apocalypse' in which at least one million dead fish were found floating in a harbour near Los Angeles on Tuesday may have been caused by a predator, strong winds or the fish simply getting lost, according to marine experts.
The mass death was welcomed by local seals and sea birds.
Firefighters sank hoses to blast the fish to the surface while others vacuumed the carcasses and scooped them into dumpsters today in a clean-up estimated to cost about $US100,000.
The fish - mostly sardines but also mackerel and anchovies - had crammed into King Harbour at the back of Redondo Beach marina, reducing the oxygen supply in the water from eight parts to 0.7 parts per million. Without enough oxygen and as the tide went out, the fish died of suffocation.
The California Department of Fish and Game, which sent samples of the dead fish to a lab for autopsies, believed the sardines simply got lost.
Spokesman Andrew Hughan said no chemical spills or oil sheens had been found. 'It is a naturally occurring - but unusual - event. It's just a mess,' he told local news.
As officials and locals removed the fish from the harbour as quickly as they could - to prevent their decomposition from attracting bacteria that will take up more oxygen and threaten the survival of other marine life, sea lions and seagulls feasted on the fish.