I dont believe that i have muskrats because my pond is like 1/4 acre and it is about 30 feet from my front door. I dont think that they would have escaped detection. Would dead roots from a tree on the other side of the dam cause my problem.
I have a better description of the problem.
The dam is mostly mowed grass. Near the water on my side of the dam there is a trail that is very similar to a mole trail that has caved in.
There is no raised area like a mole trail.
The dead tree opposite the dam is about 2 feet in diameter, elm (no mushrooms under it, dang).
It died 3 years ago and the problem was minor last year. This year I have a caved in trail that is 5 or 6 feet long. I have about 8 feet of dam left.
So,
It could be a unseen muskrat.
Roots?
There are a lot of chipmunks in that area. The neighbors cats used to keep them in check. They have become more numerous since my dog killed all the neighbors cats.