I just bought property with two ponds on it. The main pond is 1 3/4 acre. The second pond is 1/4 acre and is directly upsteam from the larger dam. I was inspecting the both dams today and noticed that the water from the smaller dam runs into a hole at the water side of the dam and exits at the base on the other side. This pond is basicly a sedement pond an is currently only about 12 inches deep. If the dam did not leak it would be about 3 feet deep. Both dams are about 25 years old and have never had any kind of drain. I juess they were designed to use the spillway.

Is there a way to fill the hole with clay soil and expect it to seal? Would mixing the soil with bentonite help? Will i have to dig from the top down to the hole and then refill? Any thoughts would be helpful