I had my waterfall running all winter and one night it got real cold and the opening at the base of the falls froze up and my pump emptied my pond. It left about 3" of water in it and of course before I could thaw out my hose to add water that water froze over. Well I still filled it up hoping that they took cover in the muck at the bottom of the pond. Well the pond finally iced out and all of my fish are swimming around like nothing happened. Next year I shut off the waterfall and just use the heater.