Going for extreme realism. I think I came close. Everything, except for the sky, is artificial.
The water is a basic cube, with minimal changes to the shape. The island is a cube, with more substantial modifications. There are 16000 trees, generated from 11 trees that were modeled separately.
The sky comes from Greg Zaal under the Creative Commons License CC-BY-SA, which I modified to a sIBL format - so I could use it as a background, lighting, and reflection source.
The render, at 10800 x 7200 px, took a little over 22 hours to render with only 500 samples. Additional post-processing in Ps took a bit longer.
I used my own water material, which is a big part of why the render took so long. After it was all said and done, I am not sure that this scene needed that complex of a node setup. I could have gone with a much more basic material and gotten the same scene, with at least half the render time.