The Pond Liner is an impermeable material that is used in the bottom part of a water body such as a fish pond, artificial river or lake to help with the retention of water. 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. Many people think a liner has but one function: to hold the water in the pond. In reality, there are other critical functions that help keep water clean and reduce the cost to build a pond / lake. Pond Liner is very effective.