Winterkill prevention efforts continue at plains lakes

“We know that they’re all tremendous fisheries, and they’re prized,” said Bobby Compton, Laramie Region fisheries supervisor. “They’re some of the best in the West.”

Winterkill refers to the dying of fish in a body of water because of a lack of oxygen.

When ice and snow cover a lake, sunlight can’t reach underwater plants, which produce oxygen through photosynthesis. Eventually, the plants die and start to decompose, which further reduces oxygen in the water to levels where fish suffocate.

The plains lakes, situated in shallow depressions carved by wind, are full of aquatic vegetation. That vegetation supports abundant insect life and in turn allows fish to grow quickly, making them great bodies of water to stock with rainbow and cutthroat trout, Compton said.

“The growth rates out there are phenomenal,” he said.

But in the winter, too much vegetation taking up the available oxygen presents a threat to aquatic life.

“It’s this double-edged sword,” he said.

Gelatt and Aslop both saw winterkill in 2016. Meeboer hasn’t seen winterkill since electricity was run out to the lake in 2012, thanks to a donation from Laramie Valley Trout Unlimited. That power is used to run an aerator, which agitates the surface of the water to prevent it from becoming completely covered with ice.

“Meeboer has permanent electricity, so the aerators are doing great out there,” Compton said.

In the fall, Game and Fish installed a 750-foot snow fence along the southwest bank of Gelatt Lake in an effort to keep some snow off the icy surface. That work was done with help from the Izaak Walton League.

Gelatt also has a solar-powered aerator, and Laramie Region fisheries biologists have tried plowing the ice to allow more sunlight into the water. Additionally, the lake is home to a sterile carp species that feeds only on vegetation, designed to reduce the plant presence.

But this winter has confounded their best efforts. Frigid temperatures combined with a few cloudy days are enough to overtake the aerator and freeze the surface. After the big snowfall in early January, the biologists couldn’t access the lake to plow. The cold temperatures that followed froze the snow so it couldn’t be scoured away by the wind.

Compton said the snow fence is doing its job, but it might not be enough to make a difference.

“I feel like we’re just experimenting out there right now,” he said. “We probably haven’t cracked the code.”

At Alsop, the biologists suspect winterkill might have a different cause, perhaps occurring later in the season as the ice is receding. They’re working with a limnologist at the University of Wyoming — someone who studies inland waters — and letting the process play out naturally this year.

At both Alsop and Gelatt, they’re taking regular measurements of oxygen levels.

Compton said avoiding winterkill is a priority for the department in maintaining the popular fisheries. They’ll know more about how the lakes fared in the spring as they complete their annual surveys.

“When we have a winterkill and you lose large fish, it takes years to get them back,” he said.