Missouri here and likewise, sometimes ponds freeze on top but only an inch or two. I've had upwards of 4 inches frozen at the top of my rain barrels and also around the outside (inside the barrel, outside of water mass). This year I have a 200 gallon tank and I'm going to build a
greenhouse around it. Since it's up against the cabin, I could always pump a little cabin heat into the
greenhouse but I don't think it will be necessary. My tank is translucent milky white so to keep the UV rays out and increase heat gain, I've got an old rubber bed mat I'm going to drape over it. If it starts to smell like rubber in the greenhouse, I'll find another way. Anything to keep the light out and make a darker surface. I've also got 4 55 gallon barrels. Those are blue and 3 of them are opaque, the other, I'll cover. Unfortunately, the black barrels seem to all be used for chemicals. My blue ones all had mocha flavoring in them originally. I plan on picking up some more barrels so that I'll have enough water mass to hold temps above freezing for a couple of days and make it an actual working greenhouse where cold weather crops can be grown all winter.
Here's some greenouse info.
http://www.extension.umn.edu/rsdp/community-and-local-food/production-resources/docs/cold-climate-greenhouse-resource.pdf
http://bradford.cafnr.org/passive-solar-greenhouse/
For something just big enough to hold one or two barrels, you could look up
solar water
heaters. Insulated walls with the front being tilted for winter sun and made of salvaged, double pane sliding glass doors. Your back wall would actually be your house.
All of the above has to be done on the south facing elevation. Keeping the barrels up off the cold ground helps for when the ground actually freezes.
And of
course, just like
solar panels, you may have to go brush the snow off for things to work.
When the rain(or snow melt) is 35 degrees F and night time temps are in the teens/twenties and daytime winds below freezing......... some sort of heat source is needed. Of course by that time, the gutters are filled with ice also but it will melt quicker than the mass of water in a tank/barrel.