Duration of the ice and snow cover is probably the more important consideration. Under 6 weeks of snow and ice cover, I wouldn't worry about it unless your pond's water quality was poor going in.

Keeping 20% of our 5 acre pond snow free can be a challenge but that is the goal. We can have 12-14 weeks of ice and snow cover and have't ever had a fish kill.

Life is Good on Bremer Pond!