Agencies conclude investigation: Contaminated runoff suspected in Garvin Brook fish kill

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Three state agencies have concluded their investigation of a fish kill in Garvin Brook, a designated trout stream in Winona County, that occurred in September 2019. The agencies — Minnesota Pollution Control Agency (MPCA), Department of Natural Resources (DNR) and Department of Agriculture (MDA) — were not able to determine the exact cause of the kill because of the time lapse between when the kill occurred and when it was reported. However, the agencies agree that the fish kill was likely caused by contaminated runoff from heavy rains that led to short-term toxic conditions for fish.

A citizen reported the fish kill on Garvin Brook at Farmers Community Park in Lewiston, Minn., on Sept. 26, 2019. DNR conservation officers investigated shortly after receiving the report. They confirmed a significant number of dead fish over about 1.3 miles of the stream.

The state agencies responded by surveying the extent of the kill, taking water samples, walking the stream and tributaries, and talking with landowners. The investigation team met several times over the following months to discuss the lab analysis of water samples and other information. They concluded that the fish were not killed by a natural cause such as disease, but by a short-duration water quality impairment.

Water quality tests conducted on Sept. 27 did not show elevated levels of pesticides or other contaminants. However, the amount of time that elapsed between the actual event that caused the die-off, its reporting, and subsequent sampling would have allowed for significant dilution in the brook, with high flows.

In September, soils in southeast Minnesota were saturated and highly prone to stormwater runoff after an extremely wet year. The area received significant rainfall, on Sept. 19-20 and again on Sept. 24-25, before the fish kill was reported on Sept. 26.

The public is encouraged to report fish kills to the State Duty Officer at 1-800-422-0798 as quickly as possible to help investigations.

For the investigation summary, visit the MPCA web site.