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Officials searching Charles River tributary in Natick area for source of foul smell and sheen on water

MassDEP investigators Thursday are searching the Stop River, a tributary of the Charles River, for the source of an apparent wastewater discharge that coated the Charles with a blue-green sheen, left a foul odor hanging in the air and may be responsible for killing fish, the state said.

Both the state environmental agency and the Charles River Watershed Association were alerted Wednesday by people travelling along the Charles between Medfield and Natick about the adverse conditions.

MassDEP sent a team of investigators out on Wednesday and narrowed the likely source to the Stop River, Ed Coletta, MassDEP spokesman wrote in an e-mail Thursday.


“Field observations and dissolved oxygen readings indicate that the source of the bad water was upstream on the Stop River, which is a tributary to the Charles River,” he wrote. “Based on visual observations including a blue/gray sheen, odors, and low dissolved oxygen content, it is possible that a discharge of untreated wastewater to the Stop River may have occurred.”

Coletta said MassDEP investigators are back in the area Thursday looking for the likely source of the untreated wastewater.

Coletta said the fish kill associated with the contamination was unlikely to be the source of the foul odor.

“While some dead fish were observed, it’s unlikely that the fish kill was significant enough to have caused the reported odors and visible impacts to the Stop and Charles Rivers,” he wrote. “MassDEP will be back out to that area today to try to determine the source of the contamination seen yesterday.’

No further information was currently available.

John R. Ellement can be reached at john.ellement@globe.com. Follow him on Twitter @JREbosglobe.