MANKATO — Dead fish washing ashore or floating on the surface is a sickening sight for most, but it’s something the Department of Natural Resources wants to hear about.
“People tend to be concerned when they find dead fish, and they can help by reporting what they see right away,” said Tom Burri, limnology consultant with the DNR who deals with water quality issues related to fisheries.
“Reporting dead fish helps us determine whether an investigation is needed.”
People should call the state duty officer, available 24 hours every day, at 800-422-0798 if they encounter several dead fish in a lake or a stream. It’s especially helpful to know what fish types and sizes people see in a fish die-off.
Several residents near Hiniker Pond were reporting a large number of dead carp in the oxbow behind the pond early last month, with most of them reporting it to Mankato and North Mankato officials.
Mankato Public Works Director Jeff Johnson said city crews pulled out about 500 dead fish, but said the area is difficult to access in many places.
“Since then, we’ve gotten some calls about the smell.”
The city contacted the state duty officer who then contacts the DNR and the Department of Health to investigate and possibly run tests to determine the cause.
Low oxygen levels during the winter are a common cause of fish kills, but a virus or bacteria also can kill fish.
Johnson said minor fish kills are fairly common in the oxbow as it has no natural source of water. Water going into the oxbow comes primarily from surface runoff in the area. If Hiniker Pond rises too high, it will send water into the oxbow as well. The water from the oxbow goes out at Butterworth Street and then to the flood-control project and into the Minnesota River.
Burri said that so far this year fish kills statewide appear to be lower than normal.
He said die-offs usually occur during winter when oxygen levels in a lake fall too much or in early summer when stressed fish that are grouped together spread deadly bacteria.
“The bacteria is in the system always. If they’re stressed from spawning or other reasons and get in close quarters with each other, it’s passed around,” Burri said. They see the bacteria-driven fish kills when the first big temperature spike hits after fish have spawned.
Dead fish sit along the edge of the ice near the public access to Eagle Lake in early spring of 2019.
When snow and ice cover a lake, they both limit the sunlight aquatic plants receive. The plants respond by reducing the amount of oxygen they produce. If vegetation dies from lack of sunlight, the plants start to decompose, a natural process that consumes oxygen dissolved in the water. Fish die if oxygen depletion becomes severe enough.
Burri said human-caused fish kills are rare but happen, usually from an accidental discharge of a toxic substance from an industry, farm, municipality or other source.
But Burri said oxygen-driven fish-kills can also have some human connections. Too many nutrients that get into lakes or streams from fertilizer or other sources spur excessive plant growth and deteriorates water quality.
“Healthy watersheds lead to health lakes.”
More information on fish kills is available on the DNR website: dnr.state.mn.us/fisheries/fishkills.html
The Link LonkApril 24, 2021 at 04:00PM
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DNR seeks public's help in reporting fish die-offs - Mankato Free Press
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