The pond was carefully shaped, even inside, to give gentle slopes for wildlife to move about on, rather than sheer sides. When you make a pond using a butyl liner, the earth below is sculpted to form the internal shape and pond shelves for plants to sit on. It's laid, with underlay, over the cavity and slowly filled, moving the liner slightly to accomodate the bends and curves. The internal ledges were covered with a layer of coarse sand to facilitate micro-organism growth and good water health. Decorative pebbles and cobbles complete the upper surfaces and provide nooks and crannies for insects to thrive in. And food for the birds... A final and important touch is to add a bucketful of gunk from an existing healthy pond. That way the micro-fauna and flora will be there to keep the water clear. PS no fish when its a wildlife pond.