The results of a 2-year study on the impact of oil discharges on the fishery resources of Lake Maracaibo, Venezuela, are presented. The lake system is described, together with relevant water quality, hydrographic, ecological, and fishery resources data. Sources of other types of pollution, domestic and industrial, are described, and their potential impact on the system are discussed. Analysis of environmental samples-water, sediments, and biota-showed low concentrations of oil in lake water and no detectable accumulation of petroleum-derived hydrocarbons in muscle tissue of selected commercial species. The occurrence of bituminous materials in the sediments, particularly in the oil production area, suggests that the natural processes of volatilization, biodegradation, and sedimentation are the major mechanisms for the removal of oil from the surface waters. Laboratory studies on the toxicity of oil indicate that relatively high concentrations of oil are required to cause mortality. Extraction of oil with lake water, however, indicated that concentrations of total light aromatic fractions were toxic in the parts per million range. The rapid loss, in a few hours, of light hydrocarbons from surface films of oil to the atmosphere was shown to reduce the toxicity to organisms significantly. Examination of the limited fisheries data available does not suggest that the resources are being depleted. However, consideration of the potential impact of nonpetroleum wastes indicates that they are contributing to the degradation of the water quality which, if unchecked, may subsequently reduce the biological resources of the lake.