I saw a beaver chewing on the bark of a twig just before it dove into this ice hole.
These pictures were all taken at Dam Number 4 Woods East in Des Plaines, Illinois.
In the thin ice above this beaver hole you can see an air bubble and a submerged branch. The brown stains are beaver droppings.
This was the cleanest of the three holes.
And now some perspective. The beaver ice holes are just past this bend of the Des Plaines.