According to a multi-agency investigation led by the Minnesota Pollution Control Agency (MPCA), several factors likely contributed to the July 2022 death of 2,500 fish in Winona County, including storm runoff, warm temperatures, and water conditions in the creek. Investigators from the MPCA, Department of Natural Resources, Department of Agriculture, and Winona County determined that the fish kill did not occur naturally, but could not pinpoint the exact cause, which is frequently the case with fish kills.
The incident which was discovered on July 26, 2022, occurred within a two-mile stretch of Rush Creek south of Lewiston, between Winona County Roads 29 and 90. Seventy-five percent of fish killed were brown trout while the remaining species included white sucker and mottled sculpin.
During the course of the investigation, field crews conducted visual observations, took field measurements, and collected water chemistry samples as well as macroinvertebrates at multiple locations near the fish kill. The investigation team also contacted more than 100 landowners located within a 10-square mile area upstream of the fish kill and conducted extensive review of manure land application records, as well as in-field land application inspections.
Investigators did not find evidence of a direct discharge of pollutants to Rush Creek.
They concluded that recent upstream applications of manure and pesticides combined with low-flow conditions in the creek prior to rainfall on July 23 may have led to the fish kill.
“We share the public’s frustration around events like this that impact hundreds of fish and oftentimes don’t point to any one cause,” said Dana Vanderbosch, assistant commissioner for water policy and agriculture. “We often hear of fish kills several hours, or even days, after they occurred and the pollution in the water has diluted and washed downstream. We have had numerous meetings with members of the community to explain challenges around these investigations, and we will continue to work with residents, businesses, and landowners on strategies to reduce the risk of future fish kills.”
While there is no direct cause determined for this event, inspections completed during the investigation uncovered violations of rules by facilities within the Rush Creek watershed. The MPCA issued notices of violation to two facilities in Lewiston for incomplete recordkeeping and violating setback requirements from sinkholes, including applying manure within 50 feet of a sinkhole and within 300 feet of a special protection area.
In 2022, state agencies received reports of approximately 150 fish kills, most of which were much smaller in scale than the Rush Creek event. Additional fish kills likely went unnoticed or unreported. Unfortunately, the exact cause of most fish kills cannot be determined, but environmental factors including those caused by human activities often contribute. Poor environmental conditions can lead to a higher incidence of disease in otherwise healthy fish populations.
To reduce the potential for fish kills, state agencies will soon launch proactive communication efforts aimed at local businesses, farmers, communities, stakeholders, and residents. The campaign will include sharing information about how to consider weather forecasts in advance of applying manure, fertilizers, and pesticides. Agencies will also work with landowners in sensitive areas and watersheds to better implement best management practices to reduce runoff to rivers, streams, and creeks.
It is critical for anyone that observes a fish kill to report it immediately to increase the chances of identifying the cause or source for a fish kill. If you see something, contact the State Duty Officer at 800-422-0798. If there is an immediate threat to life or property, call 911 first.