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STRONGSVILLE, Ohio —  It was a crisp, quiet Tuesday at the Cleveland Metroparks, but the East Branch of the Rocky River is the site of an investigation into a massive fish kill.

“Just over 28,000 wild animals have been killed.  A majority of those are minnows that were in the waterway, darters and white suckers,” said Rick Louttit, an investigator with the Ohio Department of Natural Resources.

Louttit said the fish were reported dead on Sunday.

“It may turn into a criminal investigation.  At this point, we are trying to figure out the source so we can figure out if someone has culpability.  If they threw something into a storm sewer or tributary,” added Louttit.

The fish kill encompasses a three mile stretch of Rocky River.

“I’ve been with the district for 24 years and I don’t remember a fish kill of this magnitude,” said Frank Greenland, Director of Watershed Programs with the Northeast Ohio Regional Sewer District.

On Tuesday, crews from the Northeast Ohio Regional Sewer District tested the river waters for any toxic pollutants.

“Where did this come from?  We are trying to trace back into the system to see where something might have gotten into the stream.  And also, is there any pollution?” said Greenland.

ODNR said the kill area runs from the Mill Stream Run Reservation in the Cleveland Metroparks to Wallace Lake in Berea.

At this point, they said it appeared to be contained, but still have no idea what caused it.

“We’ll continue to work on this until we exhaust all our leads.  We are working with other entities as well.  Cleveland Metroparks, Ohio EPA, Ohio Department of Natural Resources, everyone is working together to try and figure this one out,” added Greenland.