I had a major duckweed issue and hired a local company to remove it. They used a mechanical conveyor that picked up the growth and piled it on the side of the pond. They waded into the pond (they also had a small boat if needed) and skimmed the duckweed to the conveyor with a surface boom made form pool noodles. They used boat paddles to move the duckweed from the shoreline into the open water that was then collected into the floating boom tied behind them. Once they had the remaining duckweed collected from the shorelines of the pond by paddling the ductweed into the body of the pond, they moved it over to the conveyor and removed it as the final step. They sprayed a combination of an herbicide and algae control chemicals to complete the service. The cost was around $1200 as I remember for approximately 4 hours of service, 2 technicians, and the specialized equipment. I have used the suggested chemicals since to maintain minimum growth of unwanted plants after I installed an aeration system. Hope this helps.