i live in Arkansas, and although it doesnt' stay cold for long, I know what wisconsin winters are like, I grew up in michigan
anyway, here my ducks lived through 19' weather that stayed that way for a week here, now mind you the next week, it was back up to the 50's, but they did just fine,
just make sure they have a cozy place to sleep, and they can get in where it is dry and out of the wind, and they should be fine, also since the water will more than likely stay frozen up there, don't let them have anything to swim in much,
good luck

I have 2 mallards and it gets cold here in the winter. It gets below 0'. my ducks get in a dollhouse when it's cold outside, it has lots of hay in it. Most of my boy ducks would rather I throw some hay down on the ground and they sleep there! I'm sure your ducks will be fine, though. Ducks are hardy animals. They are much more stronger than a chicken or anything like that.

does anyone know where i could get mallard ducklings without ordering a minimum of 10 or more?