March 31, 2017 Shadow of the Rockies

Extended snow cover contributes to fish winterkills

Fisheries staffers in Fish, Wildlife & Parks Region 7 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.

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