We have just inherited the maintaince of a family farm. There is a pond on the property that is probably 60+ years old. Just recently we noticed that the dam area has a slow trickle on the backside. We believe it's probably an animal hole based on the location.

How can we find and fix the hole? I've read about bentonite clay, is this an option? The pond is probably about 5-6feet deep in that area.