I was really thinking about going with a much bigger pond here next year. The problem is that most of my back yard is leech field...the previous owner of the house had to add a new leech field because the original one failed. So anywhere in the yard that I can dig, I end up hitting leech field pipes and gravel. If I went above ground, does water freeze solid in zone 5 during the winter? I know my inground pool freezes, but to what depth I am not sure, it is actually raised by about 2 feet. I would love to have a larger pond 1500 gallons or so but I'm so afraid that the poor fish would freeze to death. TIA