Kai, I’m not sure if you are still active on fStoppers or not. But I’d like to compliment you on this image for the Best of Iceland Critique the Community. 27 votes and rated as 2.04 Needs Work ?! Frustrating I know I have several entries like this myself. I think your image here is fine, well balanced compositionally, wonderful exposure from the flowing water (1/8th of a second or less is my guess) no clipping in your highlight or shadows.
However when I zoom in to check details the image goes soft and I can figure other than something is amiss preparing your file for the internet. Either no or too little sharpening, too little resolution, or too much compression ?!?!