Apr 12, 2020 To make a slurry, mix the bentonite clay with water. Spread the slurry over the surface of the water. The clay sinks to the bottom of the pond and fills in the crack as it expands in size. Drain the pond. If the drain pipe is damaged or the bentonite slurry did not help the leak, drain the pond, and inspect it. Make major repairs, if necessary.There are also many products available in the market, advertised for seepage prevention or as sealants for ponds. Our 50 years of experience have taught us that bentonite is the most cost-effective solution to stop a farm pond from leaking. Bentonite is also a 100% natural clay, making it absolutely safe for fish, stock, plants, wildlife, etc.The Sprinkle Method for Bentonite Pond Sealer ... If you have an idea where the leak is originating from, such as a tree in the dam, big rock, or a layer of sand/gravel, treatment is recommended at up to five pounds per square foot of suspect area, when treating ponds with water in them.