Underground coal gasification has been in use in the Soviet Union since the 1950's and is now being developed inthe United States. Although, compared to conventional mining, UCG has environmental, health, and safety advantages, certain potential aquatic ecosystem impacts can result from release of contaminated water condensed from product gas or from contaminated groundwater reaching the surface. To assess the aquatic ecosystem hazard of UCG, we conduct chemical, aquatic-toxicity, and environmental-fate studies on a series of untreated condenser water samples obtained from several UCG experiments performed in Wyoming by the DOE. Chemical characterization showed all samples were highly alkaline with high concentrations of phenols and ammonia. Acute LC50's for fish and invertabrates ranged from 0.08 to 0.37% dilution, whereas early-life-staage bioassays with fathead minnows showed threshold effects at dilutions of 0.01%. Studies of environmental persistence and bioaccumulation potential organics in UCG condenser water samples are not complete. However, the experimental approaches used to evaluate these concern are described. From avaliable data on UCG condenser from coal conversion and other synfuel technologies. The strategy, adapted from single-compound hazard-assessment strategies, could be used as a decision making tool for regulatory agencies or to identify critical research needs related to compled effluents from coal conversion technologies.