Correct the colors and contrast of underwater photos.

1

Open the image for editing.

2

Duplicate the current layer (Ctrl+J).

Apply an "Average" filter (Filter> Blur> Average).

Invert the layer (Ctrl+I).

Change the layers' blending mode to "Overlay".

Add a "Photo Filter" adjustment layer (Layer> New Adjustment Layer> Photo Filter) and apply the following properties:

Filter: Warming Filter (85)
Density: 25-75%
Preserve Luminosity: Checkmarked

Use the "Shadow/Highlight" Tool (Image> Adjustments> Shadow/Highlight) to increase the "Highlights".

The technique final result.