A pond liner is an impermeable geomembrane used for retention of liquids, including the lining of reservoirs, retention basins, hazardous and nonhazardous surface impoundments, garden ponds and artificial streams in parks and gardens.

Pond liners need to be protected from sharp objects (for example, stones) below the liner and from being punctured by any objects in the water body. Protection can be provided with layers of sand, geotextiles (particularly needle-punched nonwovens) and other materials. Pond liners are manufactured in rolls or accordion-folded on pallets. When deployed in the field their edges and ends are overlapped and seamed together. Methods are thermal fusion, solvents, adhesives and tapes.

The edge of the pond liner is generally rolled over the top of the soil slope and secured in an anchor trench or it can be fixed to a vertical wall made of wood or concrete. Box-shaped pond liners can be made for rectangular structures. The vast majority of flexible pond liners (aka, geomembranes) are available commercially and are manufactured using the following polymers; HDPE, LLDPE, fPP, PVC, EPDM. They can also be manufactured with a fabric scrim between two plys of the polymer, e.g., PE-R, CSPE-R, fPP-R, EPDM-R, and BGM. Geomembranes can also be made in-situ by spraying a polymer (polyurea, or equal) directly on a geotextile substrate. The lifetime of these various ponds liners depends greatly on whether they are exposed or covered.^{[1][self-published source]} Clay liners can also be used which have extremely long lifetimes as long as they do not dry and crack by shrinkage and/or settlement.^[2]

• Geomembranes
• Landfill liner
• Landscape engineering
• Raceway (aquaculture)
• Raceway pond

v t e Ponds, pools, and puddles
Ponds	Ash pond Balancing lake Ballast pond Beel Cooling pond Detention pond Dew pond Evaporation pond Facultative lagoon Garden pond Ice pond Immersion pond Infiltration basin Kettle pond Log pond Melt pond Mill pond Polishing pond Raceway pond Retention pond Sag pond Salt evaporation pond Sediment pond Settling pond Solar pond Stepwell Stew pond Tailings Tarn Waste pond Waste stabilization pond
Pools	Anchialine pool Brine pool Infinity pool Natural pool Ocean pool Plunge pool Reflecting pool Spent fuel pool Stream pool Swimming pool Tide pool Vernal pool
Puddles	Bird bath Coffee ring effect Puddle Puddles on a surface Seep puddle
Biome	Beaver dam Duck pond Fish pond Goldfish pond Koi pond
Ecosystems	Aquatic ecosystem Freshwater ecosystem Lake ecosystem
Related	Aerated lagoon Bakki shower Big fish–little pond Body of water Constructed wetland Full pond Hydric soil Phytotelma Pond of Abundance Pond liner Ponding Puddle (M C Escher) Spring Swimming hole Water aeration Water garden Water Lilies (Monet) Well