Best, laziest way is to whack it back with Cutrine Plus liquid and granular (they are formulated to work in 2 different areas of the pond) and then where legal stock Tilapia to eat the new stuff that grows. We've found in Northern Indiana that stocking 40#/surface acre is needed.
Other options have been covered, but note that with an algaecide you will most likely need to retreat the pond every 2 weeks when the FA is growing.
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