We have raised pens in the barn with mortar tubs for the ducks to swim in. We've had extreme cold nights lately(single digit) and there is always quite a bit of ice build up in the tubs each morning. My question is, do they actually need water to swim in 24/7? IF so, how often do they need this. I have set up the galvanized drinking waterers in each pen for the time being. All of the pens have a heat lamp over them as well. Any feedback would be great regarding having adequate water for the ducks to swim.