SANTA ROSA, Calif. (AP) – California scientists say two recent fish die-offs in Clear Lake might not have a natural cause.

The Press Democrat reports that environmental scientists working for area tribes think a chemical spill might have killed hundreds of fish on the south end of the lake in early October.

Big Valley Rancheria environmental director Sarah Ryan says witnesses reported a chemical odor and oil sheen on the water. She also noticed that many different species and ages of fish died, which is unusual.

She expects results from water sample tests later this week and says state Fish and Wildlife officials are conducting their own analysis on fish carcasses.

Fish and Wildlife spokesman Steve Gonzalez would only tell the Press Democrat that the incidents are under investigation.