The way we assess water quality is called ‘classification’.
Classification is a useful way of reporting the health of a river or lake. For a particular point in time a classification will show us where the quality of the water environment is good, and where it may need improvement. This forms one part of the evidence base that will help us to focus our efforts on those water bodies where we need to make a difference.
Classification 2009: explanatory illustrations
Improving how we assess the water environment
The way we classify our waters is changing. For twenty years, we have been using a General Quality Assessment (GQA) scheme to assess river water quality in terms of chemistry, biology and nutrients. GQA has helped drive environmental improvements by dealing with many of the major point sources of pollutants, such as discharges from sewage treatment works or other industry. We now need a more sophisticated way of assessing the whole water environment that will help us direct action to where it is most needed.
The European Water Framework Directive (WFD) will give us the means to do this by looking at over 30 measures, grouped into ecological status (this includes biology as well as ‘elements’ like phosphorus and pH) and chemical status (‘priority substances’). The WFD covers estuaries, coastal waters, groundwater and lakes as well as rivers. We have updated our existing assessment techniques and have developed new ones for indicators we have not assessed before.
Classification results
Our classification results for each River Basin District are displayed in Annex A and B of the River Basin Plans. Also, see:
Surface waters
For surface waters there are two, separate, classifications for water bodies, ecological and chemical. For a water body to be in overall ‘good’ status both ecological and chemical status must be at least ‘good’.
Ecological classification
An ecological classification is summarised below and comprises:
- the condition of biological elements, for example fish
- concentrations of supporting physico-chemical elements, for example oxygen or ammonia
- concentrations of specific pollutants, for example copper
- and for high status, largely undisturbed hydromorphology
Ecological status class is recorded on the scale of high, good, moderate, poor or bad. ‘High’ denotes largely undisturbed conditions and the other classes represent increasing deviation from this undisturbed, or reference, condition. The ecological status classification for the water body is determined by the worst scoring quality element. The following diagram illustrates the criteria determining the different ecological status classes.
The data we used to produce our draft classification results comes largely from our own monitoring programmes. Further details on our monitoring programmes.
