Other hints: In your paint program make a new layer to work on. Starting at your waterfall top, run a guide line for your 'fall'. If that line hits any protruding rocks, stop that portion, move the guideline out to the edge of that rock and start a new fall guideline. Degree of angle from vertical will depend on 'speed' or river's flow. For distant shots a straight guiding line will do, for close-ups, you may want to make the fall have more of a ballistic curve...use an elongated oval to create your guides.

RosemaryR
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"This...this is magnificent!"
"Oh, yeah. Ooooo. Aaaaah. That's how it starts.
Then, later, there's ...running. And....screaming."