It's possible that it's a flooded open pit mine, but where are the roads or railway to get the stuff out. This body of water is sitting in a pretty isolated location. Yet anything is possible.
If we were in the U.S., I'd consider a flooded town under a reservoir, but again the size of the structures and the isolation is a detractor. How the hell did they get anything, that size, in there?
There was a lot of mining in the area in the late 1800s according to:
...but a quick scan shows nothing of that size or the same lat/lon coordinates.
I'm still not ruling out the possibility of aliens .