This dataset is part of Integrated Hydrological Units (IHU) of the UK, a set of geographical reference units for hydrological purposes including river flow measurement and hydrometric data collection. This dataset was derived from the Integrated Hydrological Terrain Model. A Catchment represents the full area upstream from a Section outlet, which is a cell upstream of a confluence of two watercourses with known names. While Sections do not overlap, Catchments can overlap because one Catchment contains Catchments for all upstream Sections. This layer currently covers Great Britain only as no dataset with river geometries and names with suitable detail is available for Northern Ireland. Full details about this dataset can be found at https://doi.org/10.5285/10d419c8-8f65-4b85-a78a-3d6e0485fa1f