Return of the native crayfish to a Welsh river

The upland rivers of rural mid-Wales supported thriving populations of Austropotamobius pallipes, the native white-clawed crayfish, until a dramatic decline began to occur around a decade ago. Crayfish plague, caused by the fungus Aphanomyces astaci, although at times a common problem in England, was not the main cause of decline in Wales. So what was the cause? Excess sediment deposition and sheep dip pollution are thought to be two of the main factors causing deterioration in the aquatic life of upland Welsh rivers. The decline and apparent recovery of A. pallipes populations in the Afon Edw, a tributary of the River Wye coincide with changes in sheep dip use as specified by the Environment Agency. In an effort to measure the amount of sediment being deposited into the Edw, specialised traps were positioned along the length of the river. Results collected so far suggest that excess sediment deposition remains a threat to A. pallipes and other organisms in the Afon Edw despite measures taken to reduce it