Many ponds composed of a variety of soil types are prone to water loss by seepage. This water loss can be controlled by the application of a western sodium bentonite clay called Pond Sealer... a high swelling, chemically unaltered, sodium bentonite that contains no additives. Sodium bentonite is a natural clay which has the characteristic of swelling many times its dry size when it becomes wet. When bentonite is applied in a layer of porous soil or mixed with a porous soil, and moistened with water, it forms an impermeable layer. When properly applied, bentonite does not affect the water or wildlife. Pond Sealer is NSF Certified. See the Pond Sealer website for more information.