Introduction to pond liners

The seal of a pond or lake is similar to the foundation of a building; what happens here affects everything above the liner or seal. Most people think a pond liner has but one function: to hold the water in the pond. In reality, there are other important functions that help keep water clean. We do not need to get into the science of sediment chemistry here since the intent of this discussion is simply to help people decide what method to utilize to seal their pond.

As Aquatic Biologists we design ponds and lakes everyday. Since we do not market pond liners we offer this guide in the public’s interest. This sets us apart from most people in the pond and lake industry. Our profession is to develop the best man-made aquatic habitat; it isn’t to sell any products.

Different pond liners for different ponds

To select an appropriate pond liner, the goals of the pond or lake project need to be considered carefully. Aspects of the pond such as size, quality goals, budget, property value, species of fish, longevity, geology, wildlife, maintenance and the level of knowledge of the pond designer need to be considered. The following section describes the benefits and weaknesses of three categories of pond liners. 

Pond liner longevity is a very important consideration in pond liner selection. Sealing ponds with clay tend to last at least centuries due to the inorganic mineral nature of clays that survive through geologic time much like their parent rock material. Synthetic pond liners usually have a twenty year warranty because they break down with exposure to sun and soil processes. While it is good for the pond liner manufacturers to offer a replacement liner, much more work is required to reinstall it if the goal is a pond to last a lifetime. Few unprotected plastic or rubber pond liners stand up to sharp animal claws or hooves, nor should the manufacturers be expected to support their products under these circumstances. Pond owners need to forecast their need for longevity in order to make an appropriate selection.

Rubber pond liners or plastic pond liners are relatively inexpensive for small ponds. They also are not generally expected to last more than ten years in a casually constructed or poorly designed garden pond that is exposed to animals with sharp claws. Protecting the synthetic pond liner with soil, sand or smooth rock will protect the pond liner enough to likely double the life expectancy of the pond liner. Consider that extra care and a couple more layers of protective underlayer need to be employed to prevent damage to the liner during pond construction. If you know you will build a more permanent pond later then a plastic liner may be the way to go in the interim. If you are building something to last a lifetime, then one of the enhanced earth or clay pon