After decades of efforts by the agricultural and scientific communities to manage the impacts of farming through Best Management Practice (BMP) implementation, there is a need to communicate to program managers and policy makers how effective these practices actually are via their expected effects on aquatic ecosystems. Land managers, biologists, funders, and policy makers could all greatly benefit from how to account for factors that influence reductions in compounds accomplished by BMP projects, to set expectations for physiochemical and biological community responses. To date there have been a great deal of studies on how BMPs may relate to nutrients and sediment in streams, and there is some professional consensus on expected outcomes on water chemistry. Studies based on observational and/ or modelled data have yielded very broad ranges of 0–92% reductions in nitrogen compounds, 0–91% in phosphorus compounds, and 0–90% in total suspended sediments; these ranges make it difficult to choose values for reliable models and predictions. Uncertainty in expected abiotic responses to BMP implementation also implies a potentially broad range of biotic responses. In this review, we synthesize results from studies investigating how the application of agricultural BMPs affect the water quality and ecological integrity of nearby water bodies and provide suggestions for monitoring BMP projects to better understand the effects of these practices. The objective of this review is to compare study results on BMP effectiveness as well as to contribute information for decision-making on BMP implementation. Our synthesis highlights the high variability in reported BMP impacts and, subsequently, the need for single studies to be interpreted with caution. We conclude with recommendations for land management and further studies of BMP effectiveness.