Extended Snow Cover Contributes to Fish WinterKills
By Toby Trigger

Posted: April 1, 2017

Fish die from a variety of factors during the winter on Montana Lakes.  This years deep snows though seems to have had a greater impact than average in eastern Montana.

According to Fisheries staffers in Fish, Wildlife & Parks Region 7  they are starting to see fish winterkills in lakes and ponds throughout the region, but they attribute it to the heavier snowfall the area has seen this winter.

“It’s kind of a normal thing for Eastern Montana when you get a winter with the kind of snow we’ve had,” said Regional Fisheries Manager Mike Backes.

But it is shaping up to be an above-average season for winterkill, according to Backes.

“We went into winter with such low water volume, and then the snow came early and stayed,” he said.

There is a common misconception that winterkill results because the entire water column freezes in a pond, Backes noted, but that does not happen. Instead, fish die from a lack of dissolved oxygen in the water. Snow covers the ice and cuts out light, which prevents aquatic vegetation from producing oxygen through photosynthesis. Vegetation begins to die and decay, which consumes more oxygen, and eventually fish die from inadequate oxygen levels. The effect is worsened by low water levels and duration of snow cover.

“That doesn’t mean there’s 100 percent kill on everything,” Backes noted.

For example, crews electrofished Hollecker Lake in Glendive March 29, which has some winterkill, but they also found about two dozen four-inch yellow perch and some suckers alive.

This is the first time Backes has seen winterkill at either Hollecker Lake or at Blacks Sawmill Pond near Birney, which is 20 feet deep. Other waters with known winterkill include Haughian Trout Pond in northern Custer County, Baker Lake, Grants Pond near Cherry Creek and Oil Pump Pond south of Glendive. “It’s coming from about every reach of the region,” Backes said.

Winterkill in ponds is not uncommon in this region and is no cause for alarm, but FWP likes to track how widespread it is. If people see winterkill in other water bodies, they are encouraged to call Fish, Wildlife & Parks at 234-0900.

Fish stocking in affected waters will begin with trout ponds the second week of April, followed by bass and other warm-water species between May and July.


This news release originated from the Montana Fish Wildlife and Parks Website at www.mt.gov.

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