The problem with the background is that the water is to bright. Because water absorbs light, the water should be darker than the sky. This is easy to fix, however. Add a Curves adjustment layer above the background layer, use a Rectangular Marquee tool to select the sky all the way to the horizon, and fill the selection (on the Curves mask) with black. Drag the midpoint of the curve down:
The water looks better, but another problem was created: the horizon is too hard. Adding a bit of haze to the horizon is easy. Simply click on the layer mask of the Curves layer and drag the Feather slider to the right to soften that horizon:
The water in the foreground has black streaks which do not look right to me. To further modify the water, add a Solid Color layer from the bottom of the Laters Panel. Position it above the Curves layer. Select a nice color, and remember that a Solid Color layer allows you to change the color on the fly. Option-drag a copy of the Curves mask up to the Color Fill (Solid Color) layer to replace its mask:
Next I want to thin out the blue color near the horizon and leave more blue at the bottom so as to cover those black areas of water. With black as the foreground color, select the mask of the Color Fill layer. Select the Gradient tool, choose Linear, black to transparent, and Shift-drag the gradient from the horizon to the bottom of the frame. I adjusted the layer opacity to 53%. Those black streaks in the foreground water are now reduced:
I should mention MacPhun has a great preset in their Intensify CK plugin called Gloomy Day. It is very powerful, and will darken and add punch to the background. See my May 30, 2016 blog post: The Gloomy Day Preset of MacPhun's Intensify CK. To use it, I selected all three background layers, did a Command-E to flatten just those layers, then invoked the plugin. Since the background was already rather dark and punchy, I used it at only 26%. Each Intensify preset has its own Amount slider, right within the plugin:
In Part 6 I will shift my focus back to Andrelica and demonstrate a couple things we can do to her to add a bit of realism before submerging her in Part 7.