Commercial oil shale development of the Green River Formation in Colorado, Utah, and Wyoming will probably take place within the next decade. Equal volumes of oil and retort water are expected to be produced using in situ oil shale processing. Research has been done on the acute toxicity of retort water to fish and mammals. The acute effect on fish is gill hyperplasia, primarily from the irritating effect of ammonia. Retort water did not appear toxic to dogs, rats, or guinea pigs under the acute test conditions imposed. No research has been done on the long-term chronic effect of retort water on any of these animals. A variety of schemes has been proposed for the treatment of retort water, most of which involve the removal of ammonia. This study was an attempt to find the effects of chronic low-level exposure of fish and wildlife to partially treated oil shale retort water.