Minnesota has widespread water quality impairments due to nonpoint-source pollution generated by agricultural, urban, and other human-altered lands. Mitigation of these impairments requires implementing best management practices (BMPs) that are designed to limit soil erosion and nutrient transport from lands to receiving waters. Long-term data sets of water quality and land-use history are needed to tease apart the many factors that affect water quality. In particular, data sets that span periods before and after BMP implementation are needed to determine BMP effectiveness.