Printed from: https://conservationhandbooks.com/waterways-wetlands/the-planting-and-management-of-new-ponds/preparing-for-planting/
Soil The new pond should have a layer of subsoil or similar material to provide a habitat for pond organisms and a rooting zone for plants. This layer is necessary over concrete, flexible linings and newly-puddled clay. Clay is an inhospitable substrate for most organisms, and any plants that do root are likely to damage...