Low oxygen levels in lakes are resulting in significant winterkill.
This year the sweet smell of spring will include the stench of rotting fish — thanks to a remarkably long, cold and snowy winter.
Some two dozen lakes in central and southern Minnesota have suffered some winterkill because of low oxygen levels. And the longer that ice and snow lingers on lakes, the more fish are likely to die.
“We know there’s significant dead fish,’’ said Dave McCormick, assistant regional fisheries manager in St. Paul. “I don’t think we’ve had this bad of a winter in 18 years.’’
And if ice and snow persist on lakes, “this could get worse,’’ he said.
Perhaps the most prominent — and surprising — lake to be affected so far is North Center near Lindstrom, where last week a patch of open water was choked with dead fish, including northerns, bass, walleyes and crappies, as well as carp and bullheads. Usually shallow lakes winterkill, but North Center is more than 40 feet deep in places and has no recent history of die-offs.
“It’s pretty shocking,’’ said Allan Nistler, 21, of Lindstrom, who fishes the lake and recently photographed the fish. Beneath the decaying rough fish on the surface were game fish, including big northerns, he said.
Other lakes where fish kills have occurred include Pelican and the north end of Maple Lake in Wright County; Little, Sunrise, Spider and north Goose lakes in Chisago County; Snail Lake in Ramsey County; Centerville Lake in Anoka County; and Long, North and South Stanchfield, Francis and Paul’s lakes in Isanti County.
Meanwhile, popular Knife Lake north of Mora in Kanabec County had low oxygen levels, so aerators have been installed.
Revealing extent of kill
DNR officials won’t know the extent of the fish kills until ice departs and they get reports of dead fish from lakeshore owners, or until they survey lakes with nets.
“As of today, we’re just preparing for the worst, and if it’s bad, we’ll be doing more fish stocking than we normally would,’’ said Jack Lauer, regional fisheries manager in New Ulm.
The brutal winter gets the blame. Fish die when oxygen levels drop too low to support them. Ice formed on lakes early and was quickly covered with snow, blocking sunlight from plants that produce oxygen. Those plants die, and the decaying matter consumes more of the limited oxygen.
If oxygen levels fall low enough, fish begin to die. Shallow lakes are most susceptible, and some suffer winterkills regularly.
Lauer said the first fish to die are game fish: walleyes, bass, panfish, perch and northern. Then rough fish such as carp, suckers and bullheads succumb.
“I’d say bullheads go last,’’ said Lauer. “If we get [dead] bullheads … we know it’s been a significant kill.’’
North Center Lake woes
That’s what officials fear happened on North Center Lake, because of the presence of dead carp and bullheads.
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