The dataset contains environmental metadata, field measurements, water chemistry data and bulk dissolved organic matter metrics from paired headwater streams and reservoirs in four anonymous UK peatland catchments. The catchments are identified as A, B, D and E, and classified as HW (headwater) or RS (reservoir). Up to six replicate samples were collected from each site during September 2023. The dataset includes site metadata (land use, vegetation cover, antecedent rainfall and air temperature), field measurements (pH, EC, water temperature), lab measurements (DOC, nutrients, metals, cations), and bulk DOM carbon, hydrogen and nitrogen ratios. Full details about this dataset can be found at https://doi.org/10.5285/ec9821dc-db7e-41e3-9670-27a841c16302