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Water quality in the Osage Creek tributary to the Illinois River was examined from fall 2007-2009 following US Environmental Protection Agency Rapid Bioassessment Protocols and Arkansas Department of Environmental Quality (ADEQ) methods at two reference and eight test sites including up- and down-stream of Rogers and Springdale, Arkansas Waste Water Treatment Plants (WWTPs). Study sites were in the Springfield Plateau of the Ozark Plateaus ecoregion. Comparison of test sites with reference streams indicated generally depressed environmental quality below WWTPs, but nutrient concentrations and biotic indicators improved significantly downstream. While upstream and downstream sites differed, ADEQ criteria were not violated by the WWTPs. Total phosphorus was significantly related to periphyton biomass (r2 = 0.15, p = 0.006) and grazing fish densities (r2 = 0.11, p = 0.02), but not strongly. Fish and invertebrate Indices of Biotic Integrity (IBI) compared favorably with each other (r2 = 0.28, p <0.03). Critical and primary season IBIs were not different (p = 0.48-0.58). Habitat was related to IBIs as well as nutrient levels. A stepwise model of factors predicting densities of primary feeding fish selected only total phosphorus and % canopy cover (r2 = 0.29, p = 0.0006).