More than 5,000 fish have died in a discharge canal at the Oyster Creek nuclear plant in Lacey Township.
State officials said the menhaden may be drawn to the canal's warm water or are scared of a predator. But officials said there's little they can do.
Environmental Protection Department spokesman Larry Ragonese told the Asbury Park Press officials would kill the fish if they tried to remove them or if they tried to divert them to the colder waters of Barnegat Bay.
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Ragonese said the fish will continue to die if the stay in the discharge canal.