The data are from bioassay experiments from 25 river sites across Great Britain to investigate the growth response of river phytoplankton to different inorganic and organic nutrient additions and compare that to in situ nutrient concentrations. The data includes calculated growth responses to inorganic and organic nutrient additions, based on experimental incubations and background nutrient data collected from sites at the same time as water for the experimental incubations. Full details about this dataset can be found at https://doi.org/10.5285/3ca94e73-57dc-4fcd-afe2-82a4e491970a
