Punta very nice image. Thanks for shearing. All work done in GIMP.
1. I cloned out a small black object near the boat.
2. I changed the WB a little to the cool side.
3. I did a small crop of the image to move the boat slightly.
4. I made set of Luminosity mask.
5. I created a layer that I used a green to blue Gradient Map on to add color and contrast to the background. I used the Light 2 Luminosity mask to mask the foreground.