This dataset is the basis for the U.S. Geological Survey Scientific Investigations Report "An evaluation of methods for computing annual water quality loads", which utilized available data from Heidelberg University and the U.S. Geological Survey to evaluate the accuracy of various methods for computing annual water-quality loads. This dataset contains two files used in the report: "QW_FLOW.csv", which contains the water-quality sample and streamflow data used to develop water-quality load estimates, and "QW_LOAD.csv", which contains observed and estimated annual loads.