Work in Progress: The Cove

Hi everyone!  I'm hoping to elicit feedback on a piece I've been working on...

Specifically, this piece has pretty unusual perspective, and I'd like some feedback on a couple decisions I need to make...  

But first, some explanation:
This piece is part of a series I've been planning, of pieces set on an island created from my imagination.  The basic idea is inspired by Bocklin's "Isle of the Dead", which supposedly he painted when requested to paint "something to dream on."  My goal is to painstakingly create a world, and then a series of guided meditations in which that world is explored...  The paintings (and other pieces) are meant to provide visuals for the meditations, and details to enhance my ability to visualize this place.

The island is crescent-shaped, with a large tree growing in the middle.  Like this:
_______
|
|
|      Tree
|
\
  \         Docks
   ----Castle----

And this painting is meant to depict a place UNDERNEATH the castle, behind the docks.  So, these stone pillars with the interlace are supports beneath the castle, that tree is in the distance, and those smaller horizontal pillars are part of the docks.



The first thing I'd like feedback on is:
Detail 1:
 
How do these shadows look, on the sand?  Any ideas for how to change this?  
Also, I'm debating whether I should add in fish, and if I do, how many fish I should add.  Originally I was going to paint in a woman swimming underwater, but as I worked on the painting I felt more and more like the emptiness of the scene helps give it the feeling I want it to have (kind of like Myst, if you're familiar with that old game).  The water looks SO empty without any plantlife or fish, but I kind of like that...  What do you think?

Detail 2:
 

I just threw the tree and the distant mountain ridges in very quickly to get an idea for how they would look, so those colors aren't final (there will be atmospheric perspective etc).

The second (much more complicated) thing I'd like feedback on:
The next difficulty I'm coming across is that--for some terrible reason--I decided that the horizon line should be below the water line, with the looking up through the water.  I've started to portray that here, but...  I have three choices to make.  First, (1) the way it CURRENTLY is has the water cut off the way it would if the viewer is standing behind glass.  
The second option (2) is to have the water extend all the way to the top of the canvas, the way it would actually look if you were underwater.  
I'm reasonably happy with both of those options.  IF I can convey that well...  I like the challenge, but it's proving difficult to find suitable references.  For example, figuring out how reflections and refraction should look is particularly hard here, because nobody ever provides examples where the viewer is under the water looking UP at something that's standing vertically (the pillars in this case).

                 ^|       |
                /  |        |
___Water/__|Pillar|
              /\   |        |
             /  \  |        |
Viewer  /    v|        |

There should be an upside-down reflection of the bottom half of the pillar, off the surface of the water.  That I can probably work out okay.
But because of refraction, things that should be straight lines often look bent (Snell's law), and I have no idea how that would look in this case.
Do you think that if I ignore that, it would be noticable?  I don't think so, but I thought I'd better ask someone else.  But the top part of the scene should definitely be distorted somehow...  Especially if I do extend the water all the way up to the top of the canvas.  Any ideas?

The third option (which is kind of a cop-out) is to change the perspective around so that your eye-line is above the water.  That would solve literally all of my perspective issues here (or at least make it easier for me to solve the issues).
Thoughts?

Thanks in advance!