My pond is 1,000 gallons, and about 3 feet at the deepest part. I used to have turtles, but turned it into a Koi pond and just have boxies and a tortoise now. At the end of one side of the pond I used to have a section under a large bush that I would losten up about 2 feet of dirt and mix it with peat moss. Then I would add about 2 more feet of leaf litter in the Fall. Mine never hibernated in the water, only under the leaf pile. I live in NY and some winters were really cold. Most were RES, with one Eastern Painted. Hope this helps.