Taken from Diet for a Small Lake
Benthic barriers, sometimes called benthic screens or bottom barriers, prevent plant growth by blocking the light required for growth. The barriers also provide a physical barrier to growth by reducing the space available for expansion and by preventing plants from germinating. Most aquatic plants under these barriers will be controlled if they are deprived of light for at least 30 days. Barriers should be installed during low-growth periods, usually in early spring after ice-out, since dense plant growth can make installation difficult.
During the summer, barriers can be applied after physical removal of the plants. Barriers are most often used around docks, in swimming areas, or to open and maintain boat-access channels. Benthic barriers can be commercially purchased or homemade. They are usually made of materials that are heavier than water and are permeable to gases produced during the degradation of plant material. Commercial benthic barriers are made of plastic, fiberglass, nylon, or other non-toxic materials. Typical barriers from commercial vendors in New York State cover between 150 and 250 square feet. The narrow dimension ranges from 7 to 12 feet for installation in small spaces such as between docks. Homemade barriers can be opaque garden tarps with PVC pipe frames constructed to hold them in place. Barriers should be securely fastened to the bottom
Image from diet for a small lake