Looks pretty good. Only thing I can really think of is that in the picture the water seems to be flowing out of the trunk of the tree. If you have a waterfall you're going to have a continuous stream from a larger water resource, and the tree shouldn't be in the middle of the stream.
Another thing to maybe consider is having the right side of the tree more evenly proportioned with the left, unless there is supposed to be a wind or something blowing from the right hand side. I haven't done a lot if iso work though.