Mississippi River sheens mystery solved: They came from the Coon Rapids Dam

State officials say a leak of hydraulic system lubricant from the Coon Rapids Dam created two sheens on the Mississippi River this week.

They said the substance can come into contact with food and not cause harm and that drinking water is still safe.

“Three Rivers Park District, which operates the dam, has reported to the Minnesota Duty Office that during the adjustment of a dam gate Tuesday morning, a valve malfunctioned and released the substance into the river. The park district estimated about 30 gallons of lubricant spilled,” according to a statement released by Michael Rafferty, spokesperson for the Minnesota Pollution Control Agency.   

The first sheen was reported Tuesday afternoon between Coon Rapids and Fridley. It was about 25 feet wide at one point and stretched for nearly two miles.

A second, smaller sheen was detected Wednesday morning near Mississippi Gateway Regional Park, formerly known as Coon Rapids Dam Regional Park.

Responders used booms to try to keep the sheens away from water intakes for both Minneapolis and St. Paul.

Both have since dissipated. Additional samples are being tested as a precaution, but state pollution control agency officials say they are not concerned about the safety of drinking water from that part of the river.

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