Liners are used to make artificial garden ponds watertight and are installed when the pond is first excavated. To create a natural-looking pond, you'll need to disguise the liner well. Most pond liners are black -- once the pond is filled with water, they are less noticeable, but there are ways to camouflage the liner so that it looks as natural as possible.
Bury the edges of the pond liner around the perimeter of the pond in around 10 cm (4 inches) of soil. This helps hold the liner in place, as well as hiding the edges.
Grade the soil over the liner at the pond's edge with sand right up to the edge of the pond. If there is a gradual slope into the pond, continue sprinkling the sand into the gradient of the pond.
Sprinkle sand on the flat portions of the pond base, interspersing with pebbles and gravel to give a natural feel.
Place larger river stones and driftwood around the perimeter of the pond, as well as intermittently on the pond floor.
Place water lily plants in the deeper part of the pond. The lily pads will grow to cover the surface of the water and help hide the pond liner from view.