An impermeable geomembrane use for water retention, including the lining of lakes, garden ponds and artificial streams in parks and gardens. Pond liners need to be protected from sharp objects (eg stones) below the liner and from being punctured by any objects in the water body. Protection can be provided with layers of sand, concrete, fiber-matting and other materials. Pond liners are manufactured in rolls. Strips of liner can be seamed or welded together on site; and a number of flexible types, such as PVC and EPDM, can have their panels pre-fabricated together in the factory to fit the design shape of the pond.