Southwest Minnesota's snow-covered shallow lakes suffering from low oxygen, leading to dead fish

Feb. 24—WORTHINGTON — A few weeks ago, Gordy Heitkamp found dead fish floating in open water in three separate areas of Indian Lake where springs and culverts keep the lake from fully freezing.

A member of the Round Lake Sportsmen's Club, which operates aerator systems on both Indian and Round lakes, west and east of the city of Round Lake, respectively, Heitkamp was concerned. Not only did he find rough fish like carp and buffalo fish, but perch, crappies and walleyes as well.

Heitkamp and club president Bryan Foote tested the water under the ice and found the likely reason for the dead fish — the dissolved oxygen level was just over 1 part per million. Any level under 2 ppm is considered stressful, even fatal, for fish.

They reported the dead fish to the Minnesota Department of Natural Resources Fisheries office in Windom, and the DNR came out to do its own testing. A week later, the DNR tested again, this time getting a dissolved oxygen reading of .3 ppm. There was little hope any fish in the lake were still alive.

Ryan Doorenbos, DNR Fisheries supervisor, said the dissolved oxygen level is basically a litmus test for whether there will be winter kill in the area's lakes. When the amount of oxygen in the water declines to 2 ppm, it's a sign that the fish are stressed.

With the amount of dead fish already surfacing on Indian Lake, the DNR and the Round Lake Sportsmen's Club made the decision to turn off the lake's aeration system last Saturday.

"The club decided if it's going to have a winter kill to start over," Doorenbos said.

For Heitkamp, who has lived on the lake for 18 years and fished it almost exclusively, it's disappointing to see the dead fish and know there was nothing that could have been done.

The aeration system on the lake was working.

"It just couldn't compensate for all of this ice and snow," Heitkamp said.

Occasional melting and refreezing also created a lake surface that was nearly impenetrable by the sun — a foot of frozen slush, Heitkamp described. Sunlight getting through the ice is what produces the oxygen needed for fish to survive the winter.

Doorenbos said snow cover is the main driver when it comes to winter kill on area lakes.

"It cuts off the light," he said. "There's no light coming in and no photosynthesis happening."

He compared it to a savings account that purges money. A lake has oxygen, which is used up by everything under the ice — fish and plants — and if the oxygen isn't replenished, the fish and plants use up what remains until there's nothing left.

Heitkamp said he first noticed dead and dying fish in a roughly 10- by 10-foot area of open water just north of his house, where a spring feeds into the lake. He then looked in the open water near the aerator shack and found it, too, was full of dead and dying fish.

The third area he checked is a county tile that runs into the lake near Hawkeye Park. There, he found large carp and buffalo, as well as dead walleye, perch and crappies — consistent with his findings at the first two locations.

Over the past 18 years, Heitkamp said he's found a few dead crappies occasionally in the spring, but nothing like what he's witnessed this year.

With this week's winter storm bringing more than a foot of new snow to the area, and still more winter weather likely to come, it's not looking good for several of southwest Minnesota's shallow lakes.

Within the Okabena-Ocheda Watershed District, watershed administrator Dan Livdahl has been measuring dissolved oxygen levels on all three lakes — Okabena, Ocheda and Bella — since January. He has no concerns about Lake Okabena; the water depth there provides more dissolved oxygen for fish species, but he has recorded low levels in Sunset Bay, as well as lakes Ocheda and Bella.

"We were down near zero (parts per million dissolved oxygen) for about three weeks on Lake Ocheda," Livdahl said, adding that levels began to increase when the snow melted. With the new snowpack, it's likely that dissolved oxygen levels in the lakes will decline again.

Livdahl tested Lake Okabena near Cherry Point on Monday, getting a dissolved oxygen level of 7.8 ppm.

"That's a long ways from the aerator," he said. "I did an oxygen rating in Sunset Bay last week and it was less than 3 parts per million — still high enough to support fish."

At Lake Bella, dissolved oxygen recordings have been below 1 ppm since Jan. 27. A commercial fisherman who was out on the lake netting bullheads pulled up his nets to find them full of dead bullheads, Livdahl shared.

The same fisherman had pulled about 800 pounds of live bullheads from the lake in January.

Livdahl received reports of dead perch, northern, carp and buffalo fish on Lake Ocheda, and found open water near a spring by Pickerel Park to be filled with dead fish.

Livdahl anticipates there will be significant winter fish kills on both Lake Ocheda and Lake Bella based on these early findings.

"We just need to wait and see," he said.

Doorenbos said his office continues to monitor dissolved oxygen levels in lakes throughout the area. On Tuesday, he said this latest snowstorm could "push lakes over the top" if the snow cover sticks around for a few weeks.

"It all depends on how the weather behaves afterward," he said. "If the snow doesn't last that long on the ice, that may not make a big difference."

Meanwhile, there are numerous lakes that have already experienced significantly low dissolved oxygen levels — Kinbrae Lake at .3 ppm; South Shetek at 1.4 ppm; Talcot Lake at .7 ppm; Bloody Lake, Flaherty (Skunk) Lake and Pearl Lake at .8 ppm; and Little Spirit Lake at 1.9 ppm. North and South Fulda lakes, Fox Lake and Lime Lake were also below 2 ppm earlier this month, Doorenbos said.

"These are numbers, it doesn't necessarily mean that we are going to see winter kill, but we do need to keep our eyes open and pay attention to what we see on the lake," he added.

Come spring, the sight of windrows of dead fish will be a sure sign that this winter, while it hasn't been pleasant for people, has been deadly for aquatic species.

And if the dissolved oxygen levels are a predictor, Doorenbos said their division will be making contingency plans for restocking the lakes most affected.

Back at Indian Lake, Heitkamp said the Round Lake Sportsmen's Club is certainly interested in working with the DNR to restock the lake.

"Bottomline, our goal is to restock the lake according to the DNR stocking plans, and if we need to help with that we certainly will," Heitkamp said.

For information on dissolved oxygen levels on southwest Minnesota's lakes, visit

dnr.state.mn.us/areas/fisheries/windom/lakes/aeration.html

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