The menace of water weeds is reaching alarming proportions, particularly in tropical nations. The weeds block canals and pumps, interfere with hydroelectricity production, waste water, hinder boat traffic, increase waterborne disease, interfere with fishing, and prevent adequate drainage of rivers and canals. Aquatic weeds spread water snails that cause schistosomiasis; they also foster malaria, encephalitis, and other mosquito-borne diseases. Yet aquatic weeds are a free crop of great potential value. They have great potential for use as animal feed, human food, soil additives, fuel production, and wastewater treatment. This report explores the conversion of aquatic weeds to food, fertilizer, paper and fiber, and energy. As sources of fertilizer, many aquatic weeds contain appreciable amounts of nitrogen, phosphorus, potassium, and other ingredients. The weeds can also improve the texture of sandy, lateritic, and heavy clay soils. Cattle find dewatered, ensiled water hyacinth highly palatable. Researchers have found that the plants can be used to treat sewage effluent so that dissolved nutrients are recovered for reuse.