The river water quality indicator is one of the UK government's sustainable development indicators, as outlined in the sustainable development strategy Securing the Future, published in March 2005. It comprises indicators of good biological and chemical quality.
* 71% of river length was of good biological quality in 2005 compared with 67% in 2000 and 60% in 1990.
* 80% of river length was of good biological quality in 2005, compared with 78% in 2000 and 79% in 1990.
In Northern Ireland
* in 2005, 56% of monitored river length was of good biological quality, compared with 61% in 2000.
* the length of rivers monitored increased greatly between 1995 and 2000, but there was a fall in river length of good quality over this period in those rivers that were monitored in both years.
* comparisons between Scotland and the rest of the UK should be treated with caution as the data are on a different basis.
* 87% of monitored river lengths were of good quality in 2005, the same as in 2000 and 2004, using a combined classification which includes, chemical, biological, nutrient and aesthetic elements.
* changes in river length allocations and the extent of monitoring between 1990 and 2005 mean that it is difficult to draw conclusions about longer term Scottish trends.
In the UK, it is estimated that about 76% of rivers were of good biological quality in 2005. This estimate is approximate because the classification scheme in Scotland differs from that in England, Wales and Northern Ireland. It is not possible to show reliable trends for the UK because of changes in definitions and the length of river monitored.