This dataset contains the analytical results of freshwater biogeochemical samples collected on Calvert and Hecate Islands on the central coast of British Columbia, Canada, from April 2013 to December 2019. Samples were collected, approximately monthly, year round at the stream outlets of the seven largest watersheds, which are gauged as part of the Kwakshua Watersheds Observatory. The samples were analyzed for dissolved organic carbon (DOC) concentration and stable isotopes, particulate organic carbon and nitrogen (POC and PON) concentration and isotopes, dissolved organic matter (DOM) composition (via metrics of absorbance and fluorescence), total, dissolved, and inorganic nutrients, metals and major ions, water isotopes, and total suspended solids (TSS). Complimenting each water chemistry sample, we measured electrical conductivity, temperature, pH, oxidation reduction potential (ORP), and dissolved oxygen in-situ with a hand-held sensor.