The mysterious sheen that stretched over 2 miles of the Mississippi River this week has been identified as a lubricant used in the Coon Rapids Dam, the Minnesota Pollution Control Agency said Friday.
At one point, the sheen spanned from Coon Rapids to Fridley and later reappeared in a smaller area.
MPCA spokesman Michael Rafferty wrote in an email that the lubricant was “used within the hydraulic system at the Coon Rapids Dam at Mississippi Gateway Regional Park.”
The lubricant is synthetic-oil based, nontoxic and safe to use in facilities that process food, according to a product description published by the manufacturer, Lubrizol.
The discovery puts to rest a mystery that consumed environmental and health agencies after the sheen was first reported on Tuesday afternoon. A second instance of possible pollution was discovered on Wednesday.
The sheen attracted significant attention because the intakes for the Minneapolis and St. Paul regional water systems are both downstream from where the substance was spotted.
St. Paul turned off its intake and relied on other sources of water while the sheen was being investigated. A spokeswoman said in a email that the system plans to reopen the intake on Monday and will work to remove lubricant that was sucked toward a chain of lakes where it stores water before treatment.
Minneapolis briefly turned off its intake but reopened it after adjusting to use water from deeper in the river and adding extra filtration to the system’s process.
