Water's fine. The foreground is weirdly crispy, as if it was more sharpened than the rest of the photo. The title suggests that sky is composited in? With that suggestion in my mind, I have to say that it looks it. The sky seems to have a different feel to it, but of course it's farther away so a less crunchy feel is perhaps ok.
The water does look a little dark as noted, mainly because the sand is lit by... something. And the light seems to just Stop at the water's edge. The light is quite surreal.
I kind of dig the thing as a whole. It has a very science fiction feel.