"Fredy" <jas...@earthlink.net> wrote in message
news:7be7dd54.03031...@posting.google.com...
Waterfalls are usually one of the first places for algae to take hold, due
to the negligible depth of water coupled with presumably high sunlight
levels. Algae is safe as in almost any aquatic plant, and will do its part
in keeping the water healthy. Your koi may also graze on it if they can
reach it.
Jim