These data are macroinvertebrate composition and size in eight Welsh upland rivers with contrasting land-use, moorland and exotic conifer, in response to riparian deciduous leaf addition. Eight sampling reaches were chosen at two sites, Llyn Brianne (4 reaches) and Plynlimon (4 reaches). The experiment consisted of adding deciduous leaves to half of the reaches whilst the other half were maintained as a control (no addition of deciduous leaves). To characterise the benthic macroinvertebrate communities of the studied streams, Surber net sampling was used to collect monthly samples during 2013 in January (before deciduous leaf addition) and from February to April (after deciduous leaf addition) in each sampling reach. Some of the collected individuals were used to characterise the invertebrate biomass of each reach. The main goal of this survey was to examine how aquatic biodiversity responds to leaf addition in moorland and conifer forested rivers. Dr Isabelle Durance was responsible for organising the surveys, Dr Hugh Feeley and Marian Pye, were in charge of collecting, processing and sorting the invertebrate samples. The work was carried out under Diversity in Upland Rivers for Ecosystem Service Sustainability (DURESS) project (Grant reference NERC NE/J014818/1). DURESS was a project funded by the Natural Environment Research Council (NERC) Biodiversity and Ecosystem Service Sustainability (BESS) programme. Full details about this dataset can be found at https://doi.org/10.5285/d07fe8a7-d4da-43e5-834d-e1b0f4cff0ac
