Although the extensive system of rhizomes is perennial, in autumn the leaves of the reeds break away from the sheaths, which hold them in place. The dead reed stem remains in place throughout the winter (3). Reeds are still harvested for use in thatching, especially in the Norfolk Broads. Recently, there has been much interest in the potential of reedbeds as water filters; their spreading, creeping system of roots can remove nitrates and heavy metals from water (5).