You might consider investigating how deep the clay is so that you can deepen the pond to 8-10 feet. You can always repack the clay if you pop through to sand. I have no idea about the geology in your area, but my place has a thick clay layer under the top soil. Yu could also stock pile the clay and reline the pond once it is the depth you want. Just not sure how well a shallow pond will work for fish in your area. I have 25' round pond fed by a flowing artesian well, but its 8-10 feet deep in the middle.