Import the light brushes. Create a new layer and change itï¿½s blending mode to Overlay. Using one of the light brushes create a light as I did in the image below. Change the fill of the layer to 31%.
Create a new layer and change the blending mode to Overlay. Use the light brush again to create a new light. Blur this light with a 20px Gaussian Blur (Filter > Blur > Gaussian Blur). Lower the fill to 51%. Create a layer mask and mask the half upper portion of the light.
Duplicate the light layer and drag it to the left.
Create a new curves adjustment layer. Drag the curve down in order to darken the scene. Fill the layer mask with black. With a white brush paint on the bottom of the scene in the layer mask to reveal the darkening effect.
Create a hue/saturation adjustment layer. Below are the settings I used. Fill the layer mask with black and paint with white on the bottom of the scene (like I did on step 13). The reason we do this is because usually underwater should be darker and more desaturated than the rest of the scene.
Open the image “Sea”. Copy all and paste into the working document.
Create a layer mask for the sea layer. With a black brush paint in the layer mask until you have something resembling my result below.
Create a Curves Adjustment layer and clip it to the sea layer. Drag the curve up to lighten the waves.
Create another clipped Curves Adjustment layer. Drag the red curve down to make the waves bluer.
Create a new layer and clip it to the sea layer. Change the blend mode to overlay. With a 20% opacity white brush paint in the areas shown below.
Create a new layer and change the blending mode to Color Dodge. With a soft brush at 5% opacity paint with #008c29 color over the sea.
Open the image “Little Shark”. Select all, copy and paste into our working document. Convert the little shark layer into a smart object and lower the opacity to 45%. Place the little shark as shown below.
Open the image “Big Shark”. Select all, copy and paste into our document. Convert to smart object. Resize and place the big shark as I did in the image below.
Add a layer mask to the big shark layer. With a black brush at 30% Opacity paint with black the lower areas of the shark so that it appears it is submerged into water.
Create a new layer and change the blending mode to Overlay. Clip it to the shark layer. With a white brush at 20% Opacity paint over the nose and the tail of the shark to make them stand out.
Create a clipped hue/saturation adjustment layer. Increase the saturation to 57 and fill the layer mask with black. With a white brush at 100% Opacity paint in the layer mask over the mouth of the shark to make it red and bloody.
Create a new layer and clip it to the shark layer. Change the blending mode to Color Dodge. With a 1px white brush at 60% Opacity paint some lines on the portion of the shark that is above the water. This will make the shark stand out more.