I've been told that cutting through the ice to check water levels is deceiving.
As water levels drop under the ice, the ice itself drops from it's own weight. There is a "bow" in the level. The surface ice can be lost to sublimation. I have a pond that loses 3/4 inch per day during the winter, but the ice follows it down. It's only detectable by observing the shoreline ice that gets left behind.
