Development of coal gasification plants in the United States for the generation of electrical power (Spencer et al. 1982) may increase the probability of accidental spills of coal-derived phenols and monohydric cresol isomers into streams and rivers. Although Europe has experienced several accidental spills from coal fired electrical plants and phenol producing plants (Alabaster et al. 1973), more information is needed as to biological effects of cresols in aquatic ecosystems. This paper presents data on physiological effects of a phenol derivative, p-cresol, on physiological rates of a major biotic component, Spirogyra sp., in many slow-moving, low gradient streams in the United States.