Water stable isotope data (hydrogen and oxygen isotopes of H2O) for 5 river basins in Washington state and Alaska. The samples were collected in 2017 during summer baseflow season. Collection sites were distributed across each basin to represent the range of possible isotope values within the basin, but sample sites were easily accessible. This dataset is associated with the following publication: McGill, L., E.A. Steel, J.R. Brooks, R.T. Edwards, and A. Fullerton. Elevation and spatial structure explain most surface-water isotopic variation across five Pacific Coast basins. JOURNAL OF HYDROLOGY. Elsevier Science Ltd, New York, NY, USA, 583: 124610, (2020).