I bought a 6 foot galvanized fence post and drilled holes in it every 4 inches at 90 degree angles. I put bolts through the holes and essentially created an enormous rake. I had visions of pulling it with my 16 foot boat (10hp Nissan 4 stoke motor) through the water and pulling up weeds. I met with very limited success. What I found was that the big rake became so heavy the boat was no longer controlable.

I then chained a pulley to a large tree, fed a rope though the pulley and tied the rope to the rake. I had someone put the "rake" into the boat and drop in in the water where we wanted it. Then using the pulley/rope arrangement we pulled the weeds to shore. One end of the rope was tied to the "rake" the other we tied to a Polaris Ranger and used the Ranger for the pulling power. It worked pretty well for the weeds that were relatively close to shore.

JHAP
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"My mind is a raging torrent, flooded with rivulets of thought cascading into a waterfall of creative alternatives."
...Hedley Lamarr (that's Hedley not Hedy)