So I've seen this most of my life. I live in a Town with a lot of fire roads and the snowmobile club maintains them for the town. There are many Beaver ponds with the beaver dams built right up against the snowmobile bridges. Every 5 years or so the Beaver dams need to be removed because they get so large. The water goes around the bridge instead of under it. It only takes a year for the Beavers to rebuild and fill the pond again.

It's a cycle. The beavers will rebuild. They always do. Unless they trap them...