UK Upland Waters Monitoring Network (UK UWMN) site. The Afon Gwy lies to the east of Plynlimon in central Wales and forms part of the headwater system of the River Wye. The catchment area is 389 ha and rises from 380 m at the sampling station to a maximum altitude of 730 m. Catchment soils are dominated by peats and stagnopodsols. The underlying geology is Lower Palaeozoic mudstones, shales and grits of the Gwestyn and Van formations, overlain in places by locally-derived glacial drift. The catchment consists of moorland grasses, notably Molinia and Nardus, with Eriophorum and the moss Racomitrium on areas of wetter land and Pteridium on the lower slopes. The majority of this grassland supports rough grazing for sheep and in summer, on the lower land, cattle. The local area is crossed with tracks used for rally testing, one of which passes through the southern edge of the catchment. Some data are managed by UK ECN Data Centre. Note: The area is the size of the catchment. Note that Afon Gwy is within the Plynlimon Experimental Catchments (see http://data.lter-europe.net/deims/site/EXPEER-UK-02).