The dataset contains a diverse range of environmental data ranging from estuary properties including geomorphology, water depth and habitat characterisation to detailed time series of parameters such as salinity and chemical and nutrient concentrations. The data are stored in a database containing a directory of existing data sources for estuaries; data for the broad properties of 79 UK estuaries; and detailed hydrodynamic, bathymetric, and sedimentary information for six estuaries: Blackwater, Humber, Mersey, Ribble, Southampton Water and Tamar. The data range from 1965 to 2002 and include both historic datasets and those collected during a recent effort (1997-2002) to enhance our knowledge of estuaries. Data collection employed a variety of instrumentation and techniques, including water, biota and sediment sample collection and analysis and the deployment of hydrographic instruments such as sea level, temperature, salinity and optical backscatter recorders. The Estuaries Research Programme (ERP) began in 1997 with the EMPHASYS project, which aimed to improve our understanding of processes operating in estuaries and use this knowledge to enhance broad scale modelling techniques that can be applied to estuarine processes. This work was funded by the Environment Agency/Department for Environment, Food and Rural Affairs (DEFRA) Flood and Coastal Defence Research and Development Programme. The data are managed by the British Oceanographic Data Centre (BODC) and are available on CD-ROM.