Minnesota state agencies have confirmed that a sheen spotted on the Mississippi River in Coon Rapids on Tuesday was caused by a lubricant from the hydraulic system at the Coon Rapids Dam at Mississippi Gateway Regional Park. The lubricant is officially classified as “suitable for incidental food contact,” which means it can come into contact with food and not cause harm, according to the Minnesota Pollution Control Agency.

Three Rivers Park District, which operates the dam, later 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.

The MPCA released a written statement on Friday indicating drinking water supplies remain safe, though St. Paul Regional Water Services closed an intake valve in Fridley this week as a precautionary measure, with the goal of keeping the substance from flowing into the chain of lakes that feed into an SPRWS treatment plant and ultimately the St. Paul-area water supply.

The sheen was initially reported at the Minnesota 610 bridge in Coon Rapids about 1 p.m. Tuesday and then traveled downstream. Local and state agencies responded and deployed booms to divert the sheen away from water intakes for the St. Paul and Minneapolis drinking water systems. They also gathered water samples from the river.

The Minnesota Department of Health compared a sample of the lubricant with water samples from the river to confirm the cause of the sheen. Additional drinking water samples have been taken and are being processed.

A smaller sheen was reported on the river in Coon Rapids on Wednesday, but no additional sheens have been seen since Wednesday.

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