I apologize if this was posted here in years past, but I just happened to run across this video on YouTube today (heck, it may even be a member's pond) of a beaver dam failing and basically draining out a pond.
I found this video to be absolutely amazing. Not just that they (the beavers) could terraform such a large section of land, but that they stuck with it over so many years and continued to add to the dam. I don't know if the land owner in this video was saddened or relieved when the dam went, but I have to admit, seeing that pond drain out was a little heartbreaking.
I'm sure folks here have their own tales to tell around beavers and ponds. This was just a eye-opener to me though...
/clayton