So create a new layer and begin to paint. I decided to paint Yellow fish.

Aqua pure illustration

Man, it's just isn't enough for me) –I really don't like the how the substance of the water looks. Create e new pattern layer clicking an icon in the lower LAYER box.

Aqua pure illustration

Fill it with any pattern that looks like clouds or has Rounded shapes. Actually there are many patterns that fit our example in standard PS pattern set. I have chosen this one .set layer Blending
 
options to Soft Light.

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and here it is

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Now go to the Layer>Add Layer Mask and choose REVEAL all and use the black–to–white Gradient from down to up to hide the effects in the lower corner .

You can see where there effects will be hidden in the Channels menu.

Aqua pure illustration

Switch to Layers menu box and view the results.