Thanks for the replies :-)
@archonforest: Yes, indeed. Hence this is my 'Junk-Thread' I post images of scenes, that I am working on and will not continue. For this image the atmosphere, PoV and surface were a 2h playing with settings. And after a while I got bored by optimizing the water's and fake stones' appearance.
So mostly, in this thread, do not expect HiRes-Renders ;-)