The only reason I say fighting DW is futile is it rides in on everything, turtles, ducks, frogs, geese, etc. If you have an investment pond or swamp nearby. In my big pond, it doesn't last a second due to the Koi and low nutrients. My garden pond is the other way around. Heavy nutrients, DW from hell, and too small for Koi. Rake it all out and it is back full coverage in a few days.

No offense taken whatsoever, as with everything to do with ponds, it depends. Many of you have far more experience than I do with these things, so take my advice with some salt, thus my signature.