LOS ANGELES -- Three weeks after a huge fish die-off in Southern California, officials said Thursday they have a body count but still can't say what drove 175 tons of sardines into the marina where they died.

As many as 2.5 million sardines created a silvery blanket on the surface and floor of King Harbor Marina on March 8, said Dave Caron, professor of biological sciences at the University of Southern California.

Several theories have been offered about the unusual behavior. Some said the sardines were lost. Others suggested the fish had been chased by marine predators or ingested toxins that confused them.

Redondo Beach City Manager Bill Workman said he even heard from people who believed the sardines may have sensed the coming earthquake in Japan and fled.

Once in the marina, the sardines used up all the oxygen and died. Residents who live on boats reported hearing what sounded like hail but was really fish coming to the surface gasping for oxygen.

Boats were temporarily trapped by the fish carcasses in the south Santa Monica Bay harbor that shelters about 1,400 boats.

Hundreds of volunteers and city workers scrambled to remove the remains to ease the pungent smell and the potential threat to other sea life.

They may have gotten some unexpected help from the tsunami in Japan, which caused tidal surges and helped to flush fish out of rocks and crevices, Workman said.

Oxygen levels were slowly returning to normal in the harbor in large part because the city was able to clean up the mess in less than a week. Officials estimated the effort cost between $300,000 and $500,000.

"If you go around the banks you can still see some of the fish," said councilman Bill Brand. "The water is still murky and smells, but I bet you won't be able to tell anything happened in a month."

Kathi Lefebvre, a biologist with the National Oceanic and Atmospheric Administration, who tested samples of the dead fish, determined the toxin domoic acid was not a factor.

"There were low levels of an algal bloom toxin detected in fish," she said. "Toxin levels were lower than we've seen in many other events, and in those events fish were not behaviorally impacted."

That left scientist struggling to explain the strange behavior in other ways.

"The only question that remains is why the fish jammed themselves into such a little spot?" Caron said.