Biologists say it will take at least a week to figure out what killed up to two thousand fish in a farming area along Tembladero Slough near Castroville.
State Fish and Game scientist Kevan Urquhart says he suspects something toxic was dumped into the water. The dead fish were found last week.
Water and fish samples are being analyzed by a Sacramento laboratory – but it could take up to two weeks before results are known.
The dead fish include suckers, carp, pike minnows, hitch and Sacramento blackfish.