Technical Abstract: Implementation of pesticide reduction practices to reduce pesticide usage within agricultural watersheds has the potential to reduce pesticide concentrations within agricultural streams. The watershed scale influence of pesticide reduction practices on pesticides and the biota within agricultural headwater streams has not been empirically evaluated. We evaluated the watershed scale influence of pesticide reduction practices for reducing atrazine usage on the pesticides, pesticide mixtures, and fish communities within channelized agricultural headwater streams in central Ohio.Water samples for pesticide measurements and fishes were collected in the spring and summer from a treatment stream that received pesticide reduction practices during the first two years and then did not in the last four years. We also sampled a control stream that did not receive pesticide reduction practices. Only three of 15 pesticide response variables and three of 15 fish community response variables differed between time periods with and without pesticide reduction practices. Mean differences in atrazine desethyl concentration, atrazine desethyl percent occurrence, and the number of pesticides between the control and treatment streams were greater during the time period with pesticide reduction practices than the time period without pesticide reduction practices. Mean differences in fish species richness, trophic guild richness, and species composition similarity between the control and treatment streams only occurred in the summer. Our results suggest that implementing pesticide reduction practices to reduce atrazine usage within small portions of the watersheds of channelized agricultural headwater streams may not influence pesticides, pesticide mixtures, and fish community structure during the spring and summer.