The Delaware County Hazmat Team and environmental officials are investigating a possible spill in the West Branch of the Chester Creek after 30-40 dead fish were found behind a pumping station on Friday.

The fish were found behind the pumping station on Mount Road in Aston Township, near Lewis Fisher Memorial Park.

A public works employee noticed the dead fish and a sheen on the water, and alerted authorities, Ed Beebe, the Delaware County director of emergency services, told CBS News Philadelphia.

Chopper 3/CBS News Philadelphia

Teams have blocked the flow of water behind the pump station and are investigating what the substance is. According to Delaware County Emergency Services, they've concluded that the substance was not petroleum-based and believed it was, in fact, chlorine-based

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