Don't let it become frozen...we have all our lillies in a 10'x10'10 pond.......they have little plastic baskets with weights and they sink to the bottom and they have been down there since 2002. I have gold fish that I put there after the water settled down for 3 days and I just feed the fish and they take care of the flowers and bugs. They get snowed on and frozen as 10 ft is deep enough not to have the roots freeze.