From what I've read, winterizing your pond and making it healthy enough for fish to survive the winter is difficult. Did you find it challenging? Many failures?
Once the temp drops below 40 degrees F (~5C) the fish go dormant, usually under some dead leaves at the bottom or in the cinderblock we have at the deep end. When ice forms they will be fine, as the bubbling pump keeps an open spot for oxygen (it should be bubbling about 1 inch above the water line and not splashing outside the pond liner). If it's a deep freeze and the pump forms an ice bubble, break it open with a hammer. The rest of the ice can stay on the pond surface.
To our surprise, every winter the pond freezes over and the fish are fine come spring. In fact they’re thriving and we don’t touch the pond at all - it doesn’t even have a pump.
The other pond could definitely do with cleaning out, but again it’s teaming with wildlife. There’s not a huge window between when the newts leave for the summer and when it freezes in winter. By the time it thaws and we think to do something about it the newts are back again.