Help with a pond
While I am located in the Western Part of the state, I see this problem often. A very effective method would be to first evaluate the site and dam of the pond in question. As you walk along the dam check for signs of crayfish (Crawldad) holes, I say this because many times these critters are the primary culprit. Next, if these organisms are not noticed then proceed to take note of other surroundings such as trees located near the spillway, dam or below the dam. Tree roots tend to grow and penetrate the dam causing leak issues. These are just a few preliminary thoughts.
Repairing each of these issues would involve extensive dirtwork to fix the issue, but this options is the only guaranteed repair method.