The Afon Crai is a river in Powys, Wales rising in the Fforest Fawr section of the Brecon Beacons National Park and flowing north into the River Usk. The headwaters known as Blaen-crai flow north from Bwlch Bryn-rhudd, a col between the Crai valley and the upper Swansea Valley for 2 km into the Cray Reservoir. The river emerges from below the dam to flow a further 8 km through the dispersed settlement of Crai (or 'Cray').