Sorry I couldn't resist messing with your pic. But I think I found the type of algae in your falls. Its Ms. Algae the Alligator lurking in there, she's just sticking her head out and drooling over your beautiful pond.
What ever it is, I hope it don't stay and you find a solution soon.
Please don't get mad that I did this, just thought it would be cute and fun.
Kim