The Mersey estuary, NW England, once had a prolific fishery but in the aftermath of the industrial revolution water quality and fisheries declined and the Mersey became infamous as one of the most polluted rivers in Europe. Until relatively recently, almost all industrial and domestic effluents were discharged without treatment resulting in abominable fouling of the shoreline, and long anoxic reaches in the upper estuary during the summer. In addition, there were unknown biological impacts resulting from a complex mixture of dangerous substances present in the river. Over 1000 million pound has been spent to remedy this situation and there is unequivocal evidence that this has had the desired effect. Dissolved oxygen is now generally >60% saturation, salmon are now found at the tidal-limit and the estuary is becoming ever more popular for sea angling. The river is no longer an embarrassing liability but is now perceived as an important asset in the economic regeneration of this region of the United Kingdom.