The National Rivers Authority's 1990 survey of water quality in England and Wales showed a 4% net decline between 1985 and 1990 (ENDS Report 201, p 6). The previous five-year survey also reported a deterioration.
In Scotland the situation is quite different (see table ). The data show a continued improvement throughout the 1980s.
In England and Wales, only 63% of river lengths were classified as good (Class 1) in 1990, and 2% were grossly polluted (Class 4). All the Scottish River Purification Board (RPB) areas have better figures than this average - even Forth, which has the most polluted rivers largely because of mine discharges. The Tay and Tweed areas have a particularly enviable record with no poor or grossly polluted lengths.
But biological indicators do not give such a rosy picture. A classification using the Institute of Freshwater Ecology's RIVPACS system puts only 78.5% of Scottish rivers in the top (Class A) category.
Biologically-based classifications will be of increasing importance in assessing the quality of Britain's rivers (ENDS Report 203, pp 10-12). The RPBs have reservations about the application of the system to Scottish rivers, and the Scottish Office is funding further research on this and the estuary classification system.
The survey covered coastal waters for the first time, and revealed that the Forth and North-East regions have the poorest quality waters. Just over 84% of coastal waters fell in the top quality class A, but 8.7% fell in the two bottom classes.