I think that the pond will be about 3 ft deep if we can make it that deep. We are using a pond liner from Lowe's and building a frame for it so that we can take it down and bring it with us when we move.with new fish ponds, most start with feeder goldfish to cycle it because they are inexpensive. They grow pretty fast. trying to purchase koi or goldfish large enough to not risk getting eaten can get pretty expensive.......I don’t have ducks, but 3 of my original goldfish have survived 2 pond reworks and 1 winter outside!