These data are surface water and groundwater chemistry collected at an urban stream in Baltimore MD, USA. This dataset is associated with the following publication: Mayer, P., M. Pennino, T. Newcomer-Johnson, and S. Kaushal. Long-term assessment of floodplain reconnection as a stream restoration approach for managing nitrogen in ground and surface waters. Urban Ecosystems. Springer Science+Business Media B.V, Dordrecht, NETHERLANDS, s11252-021-01199-z, (2022).