Break apart a bale of barley with a pitchfork or three-pronged tiller. You will need approximately 225 pounds of barley per acre of water, which is about five bales per acre.
Place the barley straw into fish netting. Don't smash the barley together tightly. The straw should just go into the net, and the net should loosely bind it together so that air can circulate through the straw. The barley requires air for decomposition, and if the straw is packed too closely together, it won't decompose quickly enough and in a way that will deter algae and other aquatic weeds.
Close the net with a tie or knot and place it into shallow water. The water should not be placed in water that is greater than 5 feet deep.
Introduce blue tilapia, redbelly tilapia or the common carp into the body of water. Using fish as a biological control is an effective and economic alternative to using store-bought chemicals and herbicides. And while barley straw has been known to prevent aquatic weeds and algae, it will not usually kill the weeds that are already present, which is why introducing these types of fish can kill the weed population already present in the body of water.