Indicator assessment
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. 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 2006, the proportion meeting criteria
for good biological quality has risen in both England and Wales and
the change is assessed as improving.
Description of trends
In England, the proportion of rivers of good
biological quality rose from 60% in 1990 to 67% in 2000 and
71% in 2006. In Wales, the proportion of rivers of good
biological quality has risen from 79% in 1990 to 82% in
2006.
In Northern Ireland, the proportion of rivers
of good biological quality has declined from 62% in 2000 to 54% 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.