Heppy, I haven't researched widgeon grass but it is closely related to sago pondweed. With that said, pulling a cable through it "may" fragment and re-root 1,000's of new stems and your 60% coverage may turn into 160% coverage. I'd check into that before you make the "pull"..
Found this... "Also like most grasses, it can produce new shoots from broken stems and roots but relies more on massive numbers of seeds. The Widgeon seeds small, greenish and pear-shaped are dispersed by water and currents. As a result, this weed can grow in incredible concentration of up to 30,000 shoots in a hectare of water."
