The Lowland Catchment Research (LOCAR) Programme field monitoring datasets provide a comparable baseline across three groundwater-dominated catchments, the Frome and Piddle in Dorset, the Pang and Lambourn in Berkshire and the Tern in Shropshire. LOCAR was a £10 million research programme which ran from 2000 to 2006, funded by the Natural Environment Research Council with additional funding from Defra, the Environment Agency and the Joint Infrastructure Fund. LOCAR brought together a multidisciplinary team of around 75 scientists and students, from 14 institutions in 12 major interdisciplinary projects. LOCAR's aim was to improve the science needed to support the management of permeable lowland catchments through an integrated and multi-disciplinary experimental and modelling programme. The two principal objectives were: one, to develop an improved understanding of hydrological, hydrogeological, geomorphological and ecological interactions within permeable catchment systems, and their associated aquatic habitats, at different spatial and temporal scales and for different land uses and two, to develop improved modelling, database and GIS tools to inform and support the integrated management of lowland catchment systems. The hydrological field monitoring included the following datasets which are available for download: Field measurements of alkalinity, chloride-ion, conductivity, pH and nutrients in rivers; Continuous measurements of conductivity, dissolved oxygen, pH, temperature and water level in rivers; Field measurements of alkalinity, chloride-ion, conductivity, pH and nutrients in rainwater; Continuous measurements of rainfall; and Continuous measurements of meteorological parameters. Supporting documentation provides information on the background to the LOCAR Programme, the sites where the data were gathered, the determinands being measured, how they were collected and analysed and the quality of the data.