Pond grass /moss

Safest way is manually rather than poison.I build a drag or rake and set it with a boat and pull it with truck tractor or what ever.you can take a length of pipe or square stock then weld pieces of rebar down it creating a rake attach a piece of chain to both ends and pull from the center with a clevis.The size is can vary but I have learned that if your drag is to small and light it will ride up and over the vegetation rather than staying on the bottom digging. Minimum 8' I'd say.Also weld your rebar in the center with equal lengths on either side of the pipe so if it rolls it will dig either direction.