First I made adjustments: channel mixer, levels, curves and color balance.
Then I made background copy and adjusted the color balance to make it all blue and green toned. I added a layer mask and used 25% opacity brush to make the green tones came out and create the "underwater look".
The last thing was layer copy with overlay blending and opacity set to 75% to make colors more saturate.
And of course cloning stamp to fix the corners.