This is a pre-release version, while CAMELS-CH-Chem is under revision. Check out the preprint at EarthArXiv CAMELS-CH-Chem is an extension of the CAMELS-CH dataset (Catchment Attributes and Meteorology for Large-sample Studies in Switzerland). It adds over 40 aggregated water quality parameters for 115 Swiss catchments from 1981 to 2020. The dataset includes time series data for more than 30 stream water chemistry variables, with hourly and daily measurements of water temperature, dissolved oxygen, pH, and electrical conductivity. It also provides (bi)monthly measurements for parameters like alkalinity (HCO₃), ammonium, calcium, chloride, dissolved and total organic carbon, dissolved reactive phosphorus, total filtered phosphorus, total hardness, total nitrogen, total phosphorus, nitrate, nitrite, potassium, magnesium, sodium, silica, and sulfate. Regarding catchment aggregated data, the dataset includes (bi)monthly stream and rainwater isotope data (deuterium and oxygen-18). Each catchment also has annual land cover data, agricultural information (crop types and livestock density), and atmospheric deposition levels of NO₃, NH₄, NH₃, NO₂, and total inorganic nitrogen.