WILLMAR -- The Minnesota Pollution Control Agency is investigating a fish kill along about 10 miles of the West Fork Beaver Creek south of Danube in Renville County.

A report of “a lot of dead fish and scummy water in Beaver Creek” was called in to the MPCA Wednesday evening.

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On Thursday morning, Hawk Creek Watershed Project and MPCA staff took dissolved oxygen readings in the creek, and Minnesota Department of Natural Resources staff took fish samples. Dissolved oxygen had dropped as low as 0.1 milligram per liter, which is 50 times below the standard of 5 mg/L. Dissolved oxygen of at least 5 mg/L is needed to sustain healthy communities of aquatic life.

Observers saw many dead fish and other aquatic life, including northern pike, smallmouth bass, creek chubs, suckers, bullheads, shiners and other minnows, as well as crayfish and dragonflies.

The MPCA believes the cause of the low dissolved oxygen is the biological breakdown of organic material, which uses up much of the dissolved oxygen in the water. The impacts were evident for about 10 miles downstream. Investigators do not believe that toxic chemicals were present.

Friday morning the state duty officer received a report from the Southern Minnesota Beet Sugar Cooperative near Renville, stating that a valve in the facility’s wastewater treatment system had been left open Wednesday evening, resulting in a discharge of “non-treated water” into county ditch 37, which goes into West Fork Beaver Creek.

The amount of untreated water released was estimated to be more than 4,000 but less than 20,000 gallons.

The cooperative’s facility holds a water quality permit from the MPCA. Discharge of untreated wastewater is not authorized by the permit.

The cooperative is working to install treatment measures, such as placing pumps to aerate water in the stream to increase dissolved oxygen levels. Other possible measures include pumping contaminated water from the stream and spreading it on land.

Treatment activities and water sampling are expected to continue over the weekend as the MPCA continues to investigate.