Millions of anchovies washed up dead early Tuesday in the harbor area of Redondo Beach, Calif., choking the waters in and around dozens of private boat slips in the King Harbor Marina.
Local television news footage showed the mass of dead fish, said by a police spokesman to be about a foot deep on the surface, Reuters reported.
"We're having millions of anchovies die off in our harbor," Redondo Beach police Sgt. Phil Keenan told Reuters in a telephone interview. "At this point, it's an unknown reason."
He said one possible explanation was that too many of the fish had congregated in a relatively small area, exhausting the water's oxygen supply, "but that's still to be determined."
Anchovies are prey for bigger fish and marine mammals, so large numbers might have swarmed into the harbor from deeper waters seeking shelter, he said.
Trudy Padilla, the marina's tenant services coordinator, said the dead fish suddenly began showing up overnight and that one end of the marina has been blocked off as cleanup operations get organized.
King Harbor Marina provides 850 boat slips to private vessels.