 This effect is attributed to the fact that the stream is approximately 9 kilometres long and passes down steep hills which quickly channel the rain that comes from the Atlantic.According to Cadw, a mill that once stood on the Ffrwdwyllt at Goytre was associated with the Grange of Hafod-y-porth, which belonged to the Cistercian monastery of Margam Abbey.Former coal levels in the valley have left industrial remains along the banks of the stream.