How can I control duckweed which is rapidly covering my one-half acre fish pond?

No selective chemicals control duckweed with safety to fish. Although it can be unsightly, duckweed, Lemna spp, offers several benefits to fish ponds. It provides food for fish, discharges oxygen into the water, absorbs dissolved carbon dioxide from the water, and slows down the growth of other, competing plants by shading. If you must clean your pond a bit, try skimming when duckweed gets beyond acceptable limits.  more