It could take a week _ and the smell could get a lot worse _ before crews manage to scoop and vacuum up tons of dead sardines from a Southern California marina.

Fish rotting on the floor of the shallow King Harbor marina were bloating and bobbing up Thursday as volunteers and city workers scrambled for a third day to keep up.

"They're coming to the surface, which is a virtue and a vice," police Sgt. Phil Keenan said. "The virtue is we can get them easier. The vice is they smell."

A palpable stench was in the air from the carpet of silvery corpses littering the marina and washing against the back of the enclosure.

Fifty tons of fish have been collected but at least another 30 tons are believed to remain on the marina floor, Mayor Mike Gin said.

Sunny, hot weather made finishing the cleanup a priority before the smell becomes any worse and the decomposing fish corpses feed bacteria that could reduce oxygen levels in the marina water and kill other sea life, officials said.

Volunteers and city workers netted fish from the surface and picked them by hand from the marina rocks. Keenan said several techniques were being used, including vacuuming up the bottom fish.

The cleanup came after the enormous school of sardines apparently suffocated in the harbor, possibly while seeking shelter from a predator or simply becoming lost near a breakwater late Monday.

Instead of leaving, the fish crowded toward the back and used all the oxygen in the water, marine experts have said.

California Department of Fish and Game officials have estimated that at least a million fish died.

Fish and Game experts are confident the sardines suffocated but about a dozen fish were sent to a laboratory in Rancho Cordova, where they'll be examined to see if a disease or toxin killed them, department spokesman Andrew Hughan said.

"Luckily, they're little small fish so it probably won't take long," he said.

Suggestions about why the sardines entered the marina and didn't leave have ranged from threatening predators to rough seas that forced the sardines to seek calm water. They may even have gotten lost, Hughan said.

However, the reason may remain a mystery.

"What this isn't is an oil spill or a chemical spill or an environmental disaster of any kind," Hughan said. "It's a natural fish die-off. It's kind of natural selection. It's sad but it happens."

He praised Redondo Beach for its fast response to the fishy tragedy. The city created a procedure for a rapid response after a toxic algae bloom known as a red tide killed millions of fish in 2005.

"It's the best disaster management that I have ever seen," Hughan said.

The fish are being sent to a composting center in Victorville. They are being buried and in 90 to 120 days will be ready for use as compost, said Barry Clifford, chief operating officer of Athens Services. The waste hauling company is considering selling the fish-based fertilizer to farms under the name "King Harbor Blend," he added.

Some residents had other plans for the sardines, though.

When the fish first surfaced, Daniel Hirose and John Pollock filled a couple of shopping bags with the sardines and froze them.

Hirose, 45, of Redondo Beach and Pollock, 50, of Manhattan Beach, planned to steer their 35-foot boat out of the marina on Thursday and go fishing for bonita, bass and shark using the dead sardines as bait.

"We're going to recycle them today," Hirose said.