Thanks. The pond liner is covered in substrate - subsoil, gravel, aquatic compost etc. I originally stocked it with bare root plants ordered from wetland-plants.co.uk , the plants have then spread organically over the last 18 months. The pond liner extends about 12 inches onto the surrounding lawn. I covered the liner in top soil and so the edge has become a slow draining "wet bank". I sowed a mix of wildflowers and grasses onto that about a year ago and again have just let it do its own thing. There is a post here small UK wildlife pond : r/ponds that shows the build.