My first impression when looking at this picture is just simply WOW. To find such a stunning place on earth and take a seemingly flawless picture of that place is incredibly difficult. But you have accomplished it perfectly. The exposure of the image is so spot on. I mean, just look at the sky!! It isn't too blown out or anything! Your long exposure was perfect and the enhanced contrast adds a sort of intense feeling that can't be described. I'm afraid I can't offer up any profound words of wisdom to help you improve... this picture shows that you clearly know what you're doing. I can't wait to see what else you capture!!
This is a very powerful and moving image. The bright green colors and flourishing life helps set a great mood for the viewer. My favorite part is the perspective of this picture, starting at what seems to be the base it feels larger than life. It's almost as if you traveling down the river yourself! The details you were able to able capture of the moss and algae of the rocks is absolutely phenomenal and adds to that sense of life this picture has captured so well.
Yet, I do have one problem with this picture: the water. The water in this picture is far too smooth to be believable. For, a raging river, as we all know, does not run smoothly but actually is quite hectic. Also, the water seems to be a focal point of the picture and, because of the great amount of detail that is emphasized in the rest of the image, becomes very distracting. You seem to have used some type of blur tool to do this to the water (in my opinion at least) while editing the image and "cleaning it up" and I would advise not using it as much next time. Anyway, it is still a very impacting image that helps represent the magic and power of nature. Thus, I applaud your talent! Keep up the good work.