As you can probably see, I applied a blue gradient lightly to the sky.
I then selected the plants--just with the selection box tool--and used the green channel in curves to bring in more green and darkened it.
I then selected the river between the boats and the trees with the selection tool again and darkened it slightly.
I lightened the entire image, selected the boats level and lightened it just a little.
I also added a 5 pixel border.
This was a fun image to work with! Your skillful use of different levels in the image (boats, river, trees, sky) proved to be a real advantage!