This is one of two fish ponds in my back yard. Don't worry....the pump is running 24/7 and the water is continually being pumped up then flows from the waterfall back down into the pond. All the fish are alive and well, we've just had a serious cold spell, that froze the top layer of water. Actually, I think that might help with evaporation. I have four generations of fish in this pond so I am very careful and concerned when it comes to their well being.