Doesn't really meet his challenge...sorry. There's too much subject rather than one isolated subject filling the frame. This is just my opinion. It is still a great shot!
Not what I would call "fill the frame". But then again it is. THe challenge description calls for the subject to fill the frame. So the question I have to ask is what is your subject here? Is it the tress? Is it the rocks? Is it the water? This is a technically sound and artful image. Does it meet the challenge? I would say no myself but I can't really dock a whole bunch on that because I can understand your interpretation of the challenge even though I don't agree with it. (7)
A lovely image, very strong. I am sure you will be questioned re: the "subject fills the frame" aspect of the challenge. I agonized over that myself: I had landscapes I wanted to enter (the landscape IS the subject after all, and it does fill the frame) but decided to go in a completely different direction and not fight that battle. Good luck to you with this one :-)