Dee

Dee, river, with its source in the mountains of Snowdonia National Park, to the west of Lake Bala, northern Wales, that flows generally north-east as far as Chester, England, and then follows a north-west course to the Irish Sea. The Dee is navigable, by means of a dredged channel, from its estuary, which is 23 km (14 mi) long and from 5 to 8.9 km (3 to 5.5. mi) wide, as far inland as Chester. By the 17th century, the estuary of the river was becoming choked by silt brought down along its course. This led to the decline of Chester and the rise of Liverpool (just to the north, on the Mersey) as the chief port of the area.

A sudden and catastrophic drop in oxygen levels in the river killed over 100,000 fish in July 2000. The cause was thought to be either industrial chemical contamination or the natural effects of huge volumes of mud entering the river after very heavy rainfall. Over the following six months the Environment Agency restocked the Dee with more than 50,000 fish. Ironically, the Dee had been selected as the UK's first Water Protection Zone in June 1999; the status meaning that the introduction of various chemicals and harmful substances into the Dee is strictly controlled.