Beautiful underwater scene - part 1

First of all open the image in photoshop and apply layer mask to it to hide the background.

Make a new layer. Set the foreground colour to #002156 and background colour to black. Now choose gradient tool and apply the first gradient vertically on the new layer.

Go to the channels palette and create a new channel by clicking on the icon circled in red at the bottom of the layers palette. Press D to reset the foreground and background colours. Now go to Filters > Render > Difference Clouds. Now press Ctrl F to reaaply the previous filter. Now press Ctrl T and drag the lower edge upwards almost upto the middle and then press Enter. Now take a large soft brush and paint the lower edge to remove the hard edges.

Now create a new channel in the same way and then go to Filters > Sketch > Chrome. Kepp the details to 0 and the smoothness 10. You can alter the values if you wish. Now press Ctrl T and drag the lower edge upwards almost upto the middle and then press Enter. Now take a large soft brush and paint the lower edge to remove the hard edges.

Now go back to layers palette, make a new layer and rename it as water. Now again go back to the channels palette and Ctrl Click on alpha 1 channel (on which we applied Difference clouds). If you want you can adjust the brightness by Pressing Ctrl L and applying levels on this channel. Now go back to the layers Palette and click on the water layer and fill white colour in the selection. Now change the blending mode of this layer to overlay.