Discrete data for major ions and nutrients in river water for 13 sites in the Humber catchment over the periods 1993 to 1997 and 1996 to 1997 and for 3 sites from the Tweed catchment over the period 1994 to 1997. Ions and nutrients measured were: Ammonia, Calcium (dissolved), Magnesium (dissolved), Potassium (dissolved), Sodium (dissolved), Bromide-ion, Carbon (organic dissolved), Chloride-ion, Nitrate, Nitrite, Phosphorus (soluble reactive), Phosphorus (total dissolved), Silicate (reactive dissolved), Sulphate, Carbon (organic particulate), Nitrogen (particulate), Phosphorus (total). Sites were sampled at regular weekly intervals and more intermittently during high flows (on average an extra sampling once a month per site). Samples were obtained using a wide neck PTFE bottle in a plastic covered bottle carrier (lowered from bridges where possible otherwise collected by immersing sample bottle by hand in the water as near the main flow as possible). Samples were filtered through Whatman 0.45um sterile membrane filters immediately on return to laboratory. Samples stored in sterilin tubes in the dark at 40C and analysed by Dionex DX100 ion chromatography system. Silicate reactive dissolved and Chloride-ion concentrations were determined by automated colourimetry and dissolved organic carbon concentrations were determined using a TOCsin II aqueous carbon analyser. Some samples on the River Aire were collected using EPIC automatic samplers. The analysis was carried out by members of the analytical chemistry section at York University (from April 1994 until November 1996) and at Wallingford Institute of Hydrology (September 1993 to April 1994 and December 1996 to April 1997), as part of the Land Ocean Interaction Study (LOIS). Full details about this dataset can be found at https://doi.org/10.5285/4482fa14-aee2-4c7f-9c62-a08dc9704051