If I where old enough I might well have been a curmudgeon. This image, even for a postcard attempt, suffers a severe lack of depth, lack of convergence, and I am also desperately looking for something to look at. (pun intended). No story.
Lack of depth
If you are teleshooting a scene, it obviously flattens the perspective. Not a problem, but it means the position of elements and their structure become that much more important. Since this image doesn't seem to be about position and structure, I would suggest to be careful about depth cues.
Lack of convergence
If I put straight lines along edges of contrast in this image, it goes nowhere. It goes nowhere interesting, nor is there a significant point of convergence which could coincide with the point of interest. The lines also do not coincide with perspective which would help gain a sense of depth.
The most dominant point of convergence is at the end of the rainbow on the right which leads me direcly out of the frame.
It seems this image has been cropped to the most interesting parts of the scene. But it has been cropped slightly to tight so that the elements are fighting for attention to be the subject, they aren't "in place", nor are they framed in a context. The framing also doesn't leave any room to breath for the elements. The tree in itself is useful but currently cropped to irrelevance. The bottom left rocks protrude into the frame but are obviously not part of it. The bottom right is dark which is not a problem persÚ, but then there is a bit of light rock again at the very bottom...
Because this image is confined to the "pretty" elements, it doesn't allow one to form a story of the place. What is the context? What happens if I would walk further upstream, what is beyond the rainbow, etc... yada yada fairytale yada yada. As for the combination of "pretty" and "picture": the reason we assign that combination more often than the others is because it alliterates better.
The second image looks a lot more promising. The elements of interest are now well within a single point of focus. Depending on the final image size and viewing distance of course. It also seems that there are some interesting opportunities for added structure in the background wall which might also help convergence.
Following is just a sample crop which might work:
The red lines show the obvious flow of the riverbed, the vortex shows how the structure can help the eye move into the scene and end up at the point of interest. The convergence to the right makes something of a story as the mist-in-the-dark creates something mysterious of what-would-be-up-there, what if I move further upstream yada yada fairytale yada yada. The point of interest has more room to breath. The entire image however has become divided into two halves of contrast.
I would certainly try to get closer to the scene. Say halfway, and use a more moderate telephoto. Given a 1.3 crop, perhaps even a normal 50? I also agree about the earlier remarks about water being either still or milky. Not something in between. In this case I think you made a nice balance between the green in the water and the rainbow colors. If you want to preserve that, you probably can't use the milky option. The point of interest should not fight for attention over the distracting elements which you have to cope with anyway. The dark tree on the right which is fairly much on the foreground may easily dominate the scene. If you can leave it out of the frame by moving closer, all the better. I would make sure the point of interest is sharp and contrasty. The darker tree on the bank could nicely complement the lighter tree in the opposite bank.
ps. Remember these remarks are just my opinion, even though I may have used generalizations here or there.