Lakes and Watercourses

Internationally, the most widely accepted framework for environmental indicators
is based on PSR-chains (Pressure-State-Response). Indicators are
chosen which reflect the relationship between environmental effects, and/or
there causes and measures taken. There is also a more sophisticated version,
called DPSIR (Driving forces-Pressure-State-Impact-Response). Variants of
the PSR/DPSIR systems are used by, among others, the OECD, the Nordic
Council of Ministers, the United Nations, the World Bank, the European
Union's Environmental Agency.
ASSESSMENT PROCEDURE
Measurements/data
Assessment of current conditions — indicates
environmental effects associated with
current conditions
Assessments of deviation from reference
values — indicates environmental
impact of human activity
Assessment of current conditions
Wherever possible, the scale used in assessments of current conditions is
correlated with effects on different parts of the ecosystems and their biodiversity,
or on human health (”effect-related classification”). In some cases,
the assessment is based only on a statistical distribution of national data
(”statistical classification”).
The scale is usually divided into five classes. Where the assessment is based
on effects, Class 1 indicates conditions at which there are no known negative
effects on the environment and/or human health. The remaining classes
indicate effects of increasing magnitude. Class 5 includes conditions leading
to the most serious negative effects on the environment and/or human health.
Due to wide natural variations, especially with regard to biological phenomena,
the indicated effects are not always the result of human activities, in
which case they can not be labelled as “negative”(see below).
Where the assessment is based only on a statistical distribution, there is no
well-defined relationship between effects and class limits. It should be noted
that parameters that are evaluated on the basis of different criteria cannot be
compared with each other.
Reference values
Ideally, the reference value for a given parameter represents a natural state
that has not been affected by any human activity. In practice, however, reference
values are usually based on observations made in areas that have experienced
some slight human impact. In some cases, historical data or model-
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