I could be wrong since I'm not a builder. But, to me, it looks like a narrow stretch of land with strategically placed driftwood.
It is indeed beautiful!
That's essentially what it is, no cc required. You need a strip of land where you'll want the dam, to ensure that the water can actually be at two different levels, and then it's mostly just white-ish terrain paint and lots of driftwood placed with judicious use of the move_objects, allow45degreeangleofrotation, and setquartertileplacement. I think I might have also placed a few bits of drftwood on the white wood wall shelves, so that I could have a bit more control over their vertical placement, but I don't remember for certain.
Welcome to the Dark Side...
We lied about having cookies.