I absolutely love the figure, the gesture and the use of value.
My critique is going to be based on unifying the image and working with different compositional options.
Your use of value is really good, in fact how you isolate the figure from the background, draw attention to the curve of the spine and face through only contrast, is excellent. I think it was the value that first made this image striking. The color though, is monochromatic. All of the hues are in the same family, and that really flattens the emotional depth of the image. That light blue you have chosen for the figure is excellent, but I want something more warm, The rest of the water seems slightly more warm, closer to indigo, but for no reason, it is not reflected anywhere in the surroundings or the background. Basically I would warm up that background, shift the hues a little more violet, play with patches of color, thing the residual hues of sunset applied to a distinctly nighttime lighting scheme. Also some warms in the shadows of the figure wouldn't hurt, opposite of what we expect with naturally warm skin tones in warm light. Don't mess with the values of the dress though, the softness of those folds is BEAUTIFUL.
The composition is okay, but I don't think it really accents the concepts you have going, nor do I think the difference in quality between your foreground and your background does you any favors. The brightly lit water around her goes directly into the darker water, which is of even tone, this really flattens the image. The largest light (for my sake I'm going to call it the moon, as that was my first impression, with the rest being the night sky) looks like a single soft brush spot, give it the same love and attention as the figure. Same goes for the other spots of light.
If I were to rework the composition, I'd go for a distinct perspective on the figure and a strong vertical layout. She is interacting with the moon, and I really want to feel that height and that strength. I'd bring the bottom of the image way down, so we can see the difference in widths of the lighter water, showing the perspective. This also gives you the opportunity to do some really great things with reflection (the possibilities) and transparency.
All on all a great image, but the character could be better integrated with her environment, and with her composition.