Minnesota authorities are investigating a recent incident that saw at least 2,500 fish, mostly brown trout, killed.
Multiple departments in the state launched an investigation into the event, which occurred last week. While the cause is still unclear, authorities and local anglers believe it resulted from fertilizer runoff from nearby farms.
“Field crews from the three agencies have collected fish and water samples and are analyzing results to help determine the cause of the fish kill,” MPCA spokesperson Mike Rafferty said.
Similar fish kill events have previously been linked to fertilizer and pesticide runoff after rain storms. In late July, the state saw heavy rainfall around the same time the incident occurred.
According to reports, as many as 500 of these die-off events happen each year. Most of them, however, are attributed to natural causes such as warm water temperatures and low dissolved oxygen levels.
Human-caused kills are usually the result of toxic chemicals, fertilizers, pesticides, or some other pollutant spilling into the water.
Moreover, agencies report that when a die-off event seems only to impact one species or size range, it’s usually the result of some disease or other natural cause. But when the die-off includes multiple species and size ranges, human activity is more likely the cause.
The Minnesota fish kill on or around July 23 affected 75 percent of brown trout. According to the Rochester Post-Bulletin, the rest of the population were warm-water species such as suckers.
Minnesota fish kill has local anglers calling for more regulations
Although next year’s stockings should help undo some of this damage, this hasn’t kept some advocates from expressing their frustrations. John Lenczewski, the executive director of the Minnesota chapter of Trout Unlimited, and Mark Reisetter, the vice chairman of the TU chapter, told reporters that many are frustrated by these die-off events.
Over the last five years, they’ve witnessed at least one trout kill per year in that region of Minnesota.
Reisetter told reporters he could smell manure in the days leading up to the July 23 rainstorm. He added that some of the dead fish were found in grass, signifying that they died when the river was higher.
On Tuesday, MPCA spokesperson Lauren Lewandowski confirmed that the event was not a natural event.
“We may not be able to pinpoint [the cause] due to the nature of the river and flowing water,” she said.
However, she mentioned that the heavy rain that occurred on July 23 could have led to contamination in local rivers and streams.
While authorities investigate the cause of the fish kill, Lenczewski says he’s more concerned about the future. He wants local leaders to make crucial changes to protect Minnesota’s trout streams.
“What we want is to see something happen,” Lenczewski said. “If it’s a question of when manure application should take place, and the rules aren’t clear enough or need to create some cushion for timing, then let’s change those rules. If it’s pesticide or fungicide application rules, well, let’s change those rules so this doesn’t continue to happen.”