Mark out the lowest part of the picture, applying the Rectangular Marquee Tool and now we have to stretch it out vertically, using next option: Edit – Free Transform (ctrl+t).

the little mermaid

Move off the marking: Select – Deselect (ctrl+d) and create now the layer's mask: Layer -Add Layer Mask – Reveal All. Then apply the Gradient Tool of black color and make the visibility of the lowest part of the layer appearing smoothly:


the little mermaid

Apply the next command: Layer – Remove Layer Mask – Apply and change the layer's Blending Mode on Screen.

the little mermaid

Then make the correction on the color of the fishes' layer (Selective Color).

the little mermaid