This report outlines the findings and progress of a project by the International Plant Protection Center to supply technical assistance for the development of an aquatic weed control program and a training course on aquatic weed control in Thailand. The program was conducted in two phases: a three-week short course and a two-week assessment of Thailand's aquatic weed problems. It was necessary for the research team to assess several factors. A thorough knowledge of the geography and climate was required as well as consideration of the natural soils, their fertility, and cultural usage. The purpose for which the water bodies are used was noted. The water quality was assessed. Finally, the assessment focused on the problem weed species itself. The assessment team came to the following conclusions: aquatic weed problems in Thai water systems are manifestations of water quality problems associated with enrichment of eutrophication; and enrichment has resulted from a combination of natural and cultural factors, including those associated with multiple usage. Irrigation systems are infested with both floating and submersed weeds which hinder or block water flow and perpetuate silting in canals. The acceleration of succession in the natural lakes is alarming, and attention should be given to elimination of both floating and submersed weeds. The present weed situation in Thailand is considered moderate but if it became more severe it would have a very detrimental effect on the economy because of the country's dependence on adequate water supplies in all areas of life. The only major water weed species not currently found in Thailand is the notorious water fern Salvinia molesta. It is now flourishing in central Malaysia. The report concludes with recommendations for long- and short-term weed control programs. The greatest short-term priority is the hyacinth problem in the Chao Phraya Irrigation Project. Suggestions are given for long-term efforts including: education, economic impact, research, monitoring and evaluation, and technical assistance. The appendices include a proposed training course, water quality data for Mae Moh Reservoir in northern Thailand, water quality data for selected irrigation tanks in northwestern Thailand, and an assessment form for water weed problems.