Sealing Leaky Ponds

Sealing Leaky Ponds

It is discouraging to have a new pond fill with water and then see it go dry within a few weeks. Leaky ponds are common in some areas of Kansas, and almost all ponds will leak to some degree, especially new ponds. In Kansas, evaporation can be expected to range from about 4 feet per year in the eastern part of the state to about 6 feet per year in the west. Most evaporation occurs during the summer, especially in hot, dry, windy periods. During this time, about half an inch of water can be lost to evaporation each day. Water loss greater than this can usually be considered leakage. The pond owner can determine his pond’s leakage rate by measuring the water level drop with a marked stick during a period of cold or very humid, calm weather. Leaks in ponds may be the result of permeable sand, gravel, or fractured rock layers that either exist throughout the basin naturally or were exposed by construction. Improper bonding of the embankment to an impermeable foundation soil can also lead to leakage. Some ponds are constructed in areas where all the soil in the basin is permeable, so the leak cannot be pinpointed. Deeper ponds tend to leak more because of the increased water pressure on the porous areas. Techniques are available to seal the leaky and potentially leaky areas. Most sealing techniques are expensive and require considerable work.

Soil Layer

If a small gravel or rock area is causing leaks, a bulldozer can be used to remove some of the problem material. The area can then be covered with a layer of soil high in clay (at least 10% clay) from some part of the basin. The added soil should be at least 1 foot thick and preferably 2 feet thick. This soil should be compacted as it is being deposited. A sheepfoot roller is recommended for serious leak areas.


Bentonite is a material that expands greatly when wet. Mixed with sand or permeable soil and water, it seeps into pores making an impermeable layer. Bentonite is usually applied at 1-2 pounds per square foot of pond bottom (more in areas over 1 feet deep). The dry powdered form creates a protective barrier when placed in a thin layer and covered with several inches of soil. Powdered bentonite can also be uniformly applied on the pond bottom and then mixed into the top 4-6 inches of soil with a disc and compacted. This method is quite successful in sealing a pond, but the seal can be punctured if cattle walk on the muddy pond bottom. A leaky pond which contains water can also be sealed by pouring a slurry of bentonite or spreading granular bentonite over the surface of the pond. This technique is usually not as successful as applying bentonite to the dry pond bottom because it is difficult to achieve an even application of the material. Bentonite is available from most feed mills or well drillers.


Trampling a pond basin with cattle or hogs will sometimes seal permeable soil. Livestock should be fenced into the pond area and fed in the dry pond basin for several months. The combination of many hooves and manure and waste feed being worked into the soil sometimes makes a seal. This is especially effective if the pond basin occasionally becomes wet. However, the pond could fill up before the basin has been completely sealed.

For ponds with rock 2 1/2 feet or more below the surface, organic matter can be used for sealing. The soil surface should be covered with about 6 pounds (dry weight) of livestock manure, straw, grass, leaves, or sawdust per square yard. An 8 inch protective layer of soil should then be placed over the organic matter. A biochemical reaction will take place between the soil and the organic matter to seal the basin.


Plastic membranes which can be placed over pond basins are available. They are expensive and must be protected from rupture. If livestock are present, their access to the pond must be prevented.


An emulsion of oil-soluble resinous polymers can be used to seal a pond without draining. The effectiveness of this material varies with condition and character of the soil, water, and climate, as well as manner of application. It is expensive and is toxic to fish, but a pond treated with polymers can be restocked within a few days after the water clears.


In the past, salt was used because sodium disperses clay particles, causing them to plug pores in the soil. It is no longer recommended because of possible water contamination.