I agree that it's not current, as I have to treat man-made streams/waterfalls for Filamentous Algae (FA) too.
Remember the original question was about large bodies of water. Nutrients � primarily nitrogen and phosphorus � when in excess are directly available and allow normal background levels of algae to grow into excessive blooms. The currents in large bodies of water will distribute and dilute the Nutrients (primarily nitrogen and phosphorus) levels with less Nutrient rich waters in the impoundment. This is why you can find isolated areas with FA problems on a large lake and not have a overall FA problem. These isolated areas tend to not have enough current or less nutrient rich waters to dilute the nutrient level in those isolated areas. Also note that you can find areas where inflows of high nutrient water can cause problems in the same lake (say near a sewage discharge where the nutrient levels remain to high.
The streams, rivers & waterfalls you are encountering (while they have current) do not have this dilution process that big lakes do to prevent the FA problems.
If statement is wrong on this I will defer the blame back to my marine biology professors at Troy University. I am only passing along some of my teachings as I was trained back in the day and realize things do change. If I had not answered from my phone I would have explained why my answer was
currents in more detail the other evening.
