Indicator description
In the UK, approximately three quarters of UK rivers, by length,
were of good biological quality in 2006. Figures are approximations
because the classification schemes in Scotland differ from those in
England, Wales and Northern Ireland. It is not possible to assess
trends at UK level because of these differences and because of
changes in the length of river monitored. The assessment is
therefore based on changes in England and Wales, on a direct
comparison between the baseline (1990) and 2009.
From 2007, England monitored river water quality using a smaller
General Quality Assessment (GQA) monitoring network known as the
headline indicator network. Assessments prior to 2007 have been
recalculated based on the smaller monitoring network. Therefore,
the results reported here should not be compared with results
previously reported.
Since 1990, the proportion of rivers of good biological quality has
generally risen and the long-term change is assessed as improving.
Between 2000 and 2009, the proportion meeting criteria for good
biological quality has risen in both England and Wales and the
change is assessed as improving.
In Northern Ireland, the proportion of rivers of good biological
quality has declined from 62 per cent in 2000 to 54 per cent in
2006, although the number of rivers assessed increased
substantially in 2000.
Relevance
Rivers of good biological quality support a diverse assemblage
of aquatic invertebrates and are therefore likely to support an
associated range of other species such as fish, mammals and
birds.
Background
In England, Wales and Northern Ireland biological quality
classifications are based on surveying macro-invertebrates living
in or on the river bed. Species groups recorded at a site are
compared with those which would be expected in the absence of
pollution.
In Scotland, since 1996, an overall classification has been used
combining chemical, biological, nutrient and aesthetic
quality. Biological grading is similar to that used in the
other countries. The final allocation of the quality class is based
on the lowest class determined from chemical, biological, aesthetic
and toxicity assessments.
For this indicator, ‘Good’ in England, Wales and Northern Ireland
is taken as corresponding to classes A and B. For Scotland, ‘Good’
is taken as corresponding to Classes A1 and A2 plus ‘unclassified’
river stretches in remote uplands. Further information on these
classifications can be found via the web links.
Further development planned
New plans for monitoring water quality under the Water Framework
Directive are being developed. Indicators of water quality will be
reviewed in the light of new monitoring plans and there may be
further development or modification of this indicator in
future.