The photos are not really a good confirmation, I know. I just had my smartphone with me and the light was very bad.
But I have absolutely no doubt it was Cinclus cinclus. I watched it over a longer time period and followed it up the creek for a while. I was able to observe it from just about 7 meters away and the round body with the white chest were clearly visible. It also dived several times and afterwards it rested on a rock again for some time.