Is there a hole in the cover? I found this just today when opening our AG pool.

I drained the cover occasionally over the winter when it wasn't frozen and when it was getting deep on the cover. Early in the winter our whale (pillow) deflated. after that I noticed the water level under the cover seemed to be getting lower - I figured "we'll figure it out in the summer". Today, as I was draining the muck one last time before lifting the cover, I noticed that one area was staying wet - and the water was clear, not the brown muck that covered the rest of the cover. That's when I found the hole. Looks like a stick went through the cover. I've been pumping out pool water all winter.