Reach-scale flow classifications (ephemeral , intermittent, and perennial) based on direct hydrologic data and field (biological and geomorphological) and geospatial (climate, geographical) indicators for northeastern and southeastern United States used to build random forest models to predict flow duration class. This dataset is associated with the following publication: Gross, S., M. Eddy, K. Fritz, B. Topping, T. Nadeau, R. Edgerton, R. Mazor, and K. Nicholas. Data Supplement to Development and Evaluation of the Beta Streamflow Duration Assessment Methods for the Northeast and Southeast. U.S. Environmental Protection Agency, Washington, DC, USA, 2023.