This data set is a record of water chemistry for the stream draining the S1 catchment and bog at the Marcell Experimental Forest (MEF) in Itasca County, Minnesota. Stream water samples were usually collected every one or two weeks since 2007 as part of the long-term monitoring program of the S1 catchment. Some samples were collected weekly as part of the Spruce and Peatland Responses Under Changing Environments (SPRUCE) project, with monitoring starting during 2011 prior to initiation of experimental warming in that study (during and after 2014). Samples are measured for pH, specific conductivity, anions (chloride, sulfate), cations (calcium, magnesium, potassium, sodium, aluminum, iron, strontium), silicon, nutrients (ammonium, nitrate, soluble reactive phosphorus, total nitrogen, total phosphorus), and total organic carbon. Occasionally, stable water isotopes and concentrations of ferrous and ferric iron have been measured. More values will be added as additional water samples are collected and analyzed (concentrations and isotopes), or archived water samples are analyzed (mostly for stable water isotopes). The MEF is operated and maintained by the USDA Forest Service, Northern Research Station. The SPRUCE experiment is a multi-year cooperative project among scientists of the Oak Ridge National Laboratory operated by UT-Battelle, LLC and the USDA Forest Service, Northern Research Station, with funding from the US Department of Energy, Biological and Environmental Research Program.