The potential adverse environmental effects of an A.I.D. irrigation project in Swaziland are assessed using a "worst-case" approach, and measures for minimizing their negative impact are presented. The planned project will develop pilot irrigation schemes using various designs, technologies, and management and financing arrangements and will involve interventions ranging from dredging, dam construction, and water diversions to land clearing/forming, fencing, and access road construction. In the absence of environmental protection measures, major physical environmental impacts would include increased soil erosion and salinity and changes in water surface quality; health impacts would include a potentially dangerous increase in transmission of schistosomiasis in certain areas, increased transmission of other enteric parasites, and acute and chronic effects of pesticide and herbicide exposure. However, the incorporation of soil and water conservation measures, improved domestic water supplies and sanitation, and regulation of pesticide use can minimize these impacts. Environmental guidelines for project design, implementation, monitoring, evaluation, and training conclude the assessment; a 74-item bibliography (1958-82) is provided.