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Man-made pollution not source of foul smell, dead fish in Charles and Stop rivers, DEP says

Cyclists stopped at the South Natick Dam Park on July 12 to see the water level of the Charles River after the recent rains.
Cyclists stopped at the South Natick Dam Park on July 12 to see the water level of the Charles River after the recent rains.Matthew J Lee/Globe staff

After two days of scouring the place where the Charles and Stop rivers meet, the Department of Environmental Protection concluded that man-made pollution was not the source of a foul smell, dead fish, and sheen on the water, according to the agency.

“MassDEP was back out to that area [Thursday] to try to determine the source of the contamination, but did not find any release of hazardous materials or any kind of man-made discharge to the river,” DEP spokesman Ed Coletta wrote in an e-mail Friday.

The cause of the odor, the fish being killed, and the sheen on the water, was not determined by DEP officials.

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The Charles River Watershed Association proposed a possible answer, however.

“Our science team measured very low dissolved oxygen levels, which is likely the cause of the dead fish and terrible smell,” the association posted on its Twitter account Friday.

The association blamed the change in conditions to the recent wave of rainy days and the resulting stormwater runoff flowing into the rivers.

“Low oxygen levels in the river can be attributed to all of the heavy rain and #stormwater #pollution entering the river in the last few weeks,” the association concluded. “Excess nutrients and pollutants flowing into the river are destructive to the ecosystem and starve wildlife of necessary oxygen.”

Both the DEP and the association were alerted about the adverse conditions Wednesday by people traveling along the Charles River between Medfield and Natick.



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