Clear water that allows sunlight to reach the bottom is a necessity for filamentous algae to grow. Dark water or water muddied from heavy rain runoff will kill it temporarily, but when it clears up again it will regrow.
I have fought it in my three ponds/lakes for a lifetime. Herbicides help for a few months but will never totally get rid of it. My grandad believed in fertilizing his pond with a special granular pond fertilizer to make the water dark. It would get so black in a few days after a fertilization that a paddle would disappear from sight in less than 12 inches depth. All algae would die and the water would be free of it for a month or so. When the water cleared back up the algae would come back.
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