Is that a rhetorical question? There's quite some difference between a 200m tall concrete dam that holds 1m+ cubic decameters of water[0][1], and a bunch of twigs and logs jumbled in a creek that might be 2 meters high on average and actually house life like beavers, frogs, birds etc.[2]

[0] https://en.wikipedia.org/wiki/New_Bullards_Bar_Dam

[1] https://en.wikipedia.org/wiki/Environmental_impact_of_reserv...

[2] https://en.wikipedia.org/wiki/Beaver_dam#Benefits

The problem is that beavers didn't suddenly start doing that, the ecosystems they live in co-evolved around the existence of beavers.

On time scales relevant to evolution, human civilization is happening in an instant and nothing can adapt as fast.

The result is a gigantic loss of biodiversity.

Get back to me when beavers are causing the extinction of thousands of other species and arguing about how to warn their descendants about radioactive waste.

The point that's missing from this discussion is that beavers have been building dams for an eternity because it's part of their natural behaviour. The ecosystem has had ample time to adapt to it. An ecosystem is a delicate balance between systems that results from these systems co-evolving in the same environment for millions of years. The systems (plants animals seasonal change, climate) are all highly fine tuned to each other. Yes, this balance is sometimes abruptly disturbed under "natural" circumstances, but this is rare. What humans are doing in the last couple hundreds of years involves much more sudden changes to which eco systems have no time to adapt. It's the suddenness of the changes what's unnatural about it. Whether you call it natural or not is besides the point though. The point is that human dam building is a phenomenon very different from beaver dam building because, besides scale and impact, it did not gradually co-evolve with an eco system, but is an abrupt and disruptive change.