progressively reduce the maintained flow at Manley Hall. The overall effect of this regulation has a marked impact on the hydrograph of the River Dee. In dry years the hydrograph flat-lines at 10 m³/s whilst dry weather continues such as in 1990 Quality management The River Dee regulation system also manages a water quality monitoring and alerting system that includes real-time quality monitoring for a wide range of chemical parameters supplemented by daily fixed site monitoring with analysis provided in near real-time by a dedicated laboratory service. The results of the analysis are made available to the four participating organisations on a routine daily basis. For each of the critical water quality parameters alert levels and action levels have been set based on past experience. If an alert level is exceeded an immediate alert (DEEPOL 1) is issued to all participants. As contamination levels increase or the contaminant plug nears an abstraction point the DEEPOL level rises to DEEPOL 2 and finally DEEPOL 3 at which time the affected abstractions are closed until the river quality returns to normal. This quality management system was developed following a severe Phenol pollution of the River Dee in the 1980s which resulted in contaminated water being supplied to large areas of Liverpool and the Wirral. Contamination of raw water is a more significant problem on the River Dee because the River Dee is normally of exceptionally good quality and as a result the abstractions have been constructed directly from the river rather than via bank-side storage reservoirs as is more common when taking water from Rivers of less reliable quality. Water Protection Zone The first Water Protection Zone was established on the River Dee in 1999 as a mechanism to further safeguard the quality of the river. Although the statutory order was promoted by the Environment Agency it was supported and endorsed by the representative members of the Dee Regulation Scheme. References Bala, Gwynedd Cerrigydrudion Llandderfel Llangywer Llanrhaeadr-yng-Nghinmeirch Llanuwchllyn Llanycil River Dee, Wales River regulation in Conwy County Borough River regulation in Denbighshire River regulation in Gwynedd River regulation in Snowdonia River regulation in Wrexham River regulation in England Water supply and sanitation in England Water supply and sanitation in Wales