This dataset contains high-frequency water quality measurements taken at multiple sites in the River Frome catchment area, Dorset, UK. Water quality data consists of a mixture of 30-min sensor readings and frequent grab samples. Also included are high-frequency discharge readings at Environment Agency (EA) managed flow gauging stations and at sewage treatment work (STW) effluents. These measurements were taken between 12/08/2022 and 14/09/2022 inclusive. Measurements were recorded at multiple river sites, boreholes, and STW effluents. All sites are contained within the catchment area between the Environment Agency gauging stations located at Dorchester and East Stoke i.e., the lower part of the River Frome. In total, 24 monitoring sites exist. The data were collected for PhD project “Supporting river water-quality management by high-resolution modelling: a case study in a lowland permeable chalk catchment” awarded to Thomas Homan and funded under GW4 FRESH CDT, supported by the Natural Environment Research Council (Grant NE/R0115241). Water quality data were collected by Thomas Homan (PhD candidate at the University of Bath). Wessex Water Ltd. provided high frequency measurements of ammonium and discharge at their STW sites, borehole water quality measurements, as well as high-frequency nitrate measurements at sites: Louds Mill and East Stoke. The Environment Agency discharge data were provided under the terms of the Open Government Licence