We have discovered that there are a couple of disadvantages to running the pump during winter. One is that with ice covering the pond, it is more difficult to monitor the water level, and we don't want to run our pump dry (just in case we do develop a leak somewhere). Not a problem so far, but something we have to keep an eye on. The other problem is that when we had our first round of REALLY cold weather, the stream iced up. The water kept running easily underneath the ice, but the ice kept spreading, and spreading. It spread outside the stream at least 3 feet on either side. We lost about 2" in our water level. Again, nothing to worry about, just another reminder that maintaining a pond properly is a year round chore.