Book excerpt: This National Academy of Sciences report describes ways to exploit aquatic weeds for grazing, and by harvesting and processing for use as compost, animal feed, pulp, paper, and fuel. The book also describes utilization for sewage and industrial wastewater.Aquatic weeds have always existed, but in recent decades their effects have been magnified by man?s more intensive use of natural water bodies - his modifying them into canals and dams, polluting them with farm and city wastewaters, and introducing aggressive plant species into new locations. These plants, among the most prolific on earth, grow luxuriantly in the tropics, weigh hundreds of tons per hectare, and can be a serious hindrance to a nation?s development efforts. Eradication of the weeds has proved impossible, and even reasonable control is difficult. Turning these weeds to productive use would be desirable, but only limited research has been carried out.This report examines methods for controlling aquatic weeds and using them to best advantage, especially those methods that show promise for less-developed countries. It emphasizes techniques for converting weeds for feed, food, fertilizer, and energy production. It examines, for example, biological control techniques in which herbivorous tropical animals (fish, waterfowl, rodents, and other mammals) convert the troublesome plants directly to meat.