The object of this research, conducted between December 8, 1970, and August 27, 1971, was to assess the effect of pollution on benthic macroinvertebrates in Halfway Creek and the Mississinewa River at Albany, Indiana.Data related to macroinvertebrate composition, population density and distribution were obtained through the utilization of Surber and Coleman Pot Samplers. Physical and chemical characteristics were determined using Standard Methods to provide background data for the biological conditions encountered.Data from diversity and standard deviation indices were analyzed separately, and then combined to produce three pollution categories indicating degree of water quality degradation. The diversity index evaluated organically enriched situations but was inadequate in evaluating toxic chemical situations. The standard deviation index indicated toxic conditions, but failed to interpret population dominance satisfactorily.The indices and pollution category data indicated substandard water quality in Halfway Creek. At the confluence of the two streams limiting and selective effects of pollution produced subtle population changes of macroinvertebrates that were measurable by indices and pollution category data. Supportive data from seasonal life histories, decrease of organisms known to be sensitive to toxic and organic wastes, and chemical data indicated a decrease in quality of the Mississinewa River near the mouth of Halfway Creek as compared to its upstream condition.Ball State UniversityMuncie, IN 47306