Data are from 1,000 river and stream sites across the conterminous US where consistent biological, chemical, physical and watershed data were gathered. The sites were selected using a probability survey design so that the results provide inferences to all perennial flowing waters in the lower 48 states. This dataset is associated with the following publication: Omernik, J., S. Paulsen , M. Weber , and G. Griffith. Regional patterns of total nitrogen concentrations in the National Rivers and Streams Assessment. JOURNAL OF SOIL AND WATER CONSERVATION. Soil and Water Conservation Society, 71(3): 167-181, (2016).