Garvin Brook at Farmers Park was full of dead trout following a major fish kill last week.
by CHRIS ROGERS
Hundreds, likely thousands, of fish have died after a fish kill in Garvin Brook near Farmers Park outside Stockton, according to the Minnesota Department of Natural Resources (DNR). The Minnesota Duty Officer received a report of the fish kill last Thursday morning. The cause is still unknown. State investigators were on the scene on Thursday afternoon and Friday morning.
DNR staff collected 224 dead fish — brown trout, brook trout, and sculpin — at five sampling stations along the stream, DNR Area Fisheries Assistant Director Vaughn Snook reported. After further work to determine how much of the stream was affected, investigators will use those samples to estimate how many total fish were killed. “It’s impossible to count the entire amount of dead fish. So we set up these stations and extrapolate,” Snook explained.
“It’s not the South-Branch-of-the-Whitewater-in-2015-sized — mostly just because it’s not that big of water,” Snook said when asked how the size of this fish kill compares to others. “But it’s definitely more than a couple hundred fish. It’s probably into the thousands.”
In 2015, a fish kill on the South Branch of the Whitewater River killed an estimated 9,000-10,000 fish. State agencies said an investigation into its causes was inconclusive.
Snook said his office should have an estimate of the total number of fish killed next week. Meanwhile, Minnesota Pollution Control Agency (MPCA) staff were in the field gathering water quality data, and Snook said Minnesota Department of Agriculture investigators would be searching for potential sources of pollution that may have caused the fish kill. DNR staff will send dead fish to a pathology lab for, essentially, fish autopsies. The lab will check the fish’s organs and fat, Snook said. “They’ll try to find out what was damaged, whether gills are all singed up — like [a contaminant] burnt them — or look at stomach content,” he explained.
Snook stated he suspected pollution may have run off into the stream during a large rain event earlier last week. He explained why he suspected runoff: “I’ve never heard of a trout stream that had die offs from something internal. It’s always runoff, whether it be pesticides, herbicides, manure, sewage, or a truck rolled over and spilled ethanol.” Garvin Brook is a spring-fed stream. Snook confirmed pollutants could have also entered groundwater feeding the spring through a sinkhole or other karst feature.
At Farmers Park on Friday, dead brown trout could be seen up and down the creek. Peterson Creek, which flows into Garvin Brook at Farmers Park, did not appear to be affected by the fish kill. At press time, Snook said the DNR is still unsure how far up and downstream the fish kill extended, but that investigators should determine that shortly.
“We can’t do anything today. These fish are dead. We just have to try to figure out why and try to prevent it from happening again,” Snook stated.
Heavy rains preceded the 2015 Whitewater River fish kills, as well. Investigators eyed pesticide, herbicide, fungicide and manure applications and algae blooms as potential causes, but ultimately stated that the cause could not be pinned down. Some citizens found that result frustrating and concerning. State investigators wrote, “Scientific analysis of available evidence was unable to draw a clear conclusion as to the cause of this fish kill, as a combination of biological, chemical, and environmental conditions may have led to this event. Often these lethal combinations are ephemeral and difficult to detect after the fact, even though agency response may have been quick.”
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