Objects have been duplicated into immovables I am trying to replicate Claude Monet's bridge over a pond but everything has been duplicated into immovable objects that I can't edit or even select. 

Here's a screencap of it.

https://i.stack.imgur.com/4jMgW.jpg

And here's the .blend file.

https://drive.google.com/open?id=19hdlGl47T_9LfnlVbE81Izv3tyk5MsEC
You duplicated it outside of edit mode. Switch back to object mode and select the duplicate, then delete it. 

Objects other than the one you are currently editing cannot be modified in any way.