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Freshwater quality

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Assessment versions

Published (reviewed and quality assured)

Justification for indicator selection


  • Biodiversity relevance: the indicator gives an assessment of water quality which fundamentally determines the structure and functioning of aquatic and associated terrestrial ecosystems and dependent organisms.
  • Country comparison: the indicator is quantitative and representative of the situation in countries.
  • Well established data flow and methodology.
  • The indicator is updated annually.
  • The data are in Waterbase and are freely available through the EEA data service.

Scientific references:

  • No rationale references available

Indicator definition

This indicator shows:

1. Annual median concentrations in rivers of Biological Oxygen Demand (BOD) and ammonium (NH4).

2. Trends in concentrations of orthophosphate and nitrate in rivers, total phosphorus and nitrate in lakes, and nitrate in groundwater bodies.


The concentration of nitrate is expressed as mg nitrate (NO3)/l for groundwater and mg nitrate-nitrogen (mg NO3-N/l) for rivers and orthophosphate and total phosphorus as mg P/l.

Policy context and targets

Context description

Ammonium concentrations are normally raised as a result of organic pollution, caused by discharges from waste water treatment plants, industrial effluents and agricultural runoff. Ammonium exerts a demand on oxygen in water since it is transformed to oxidised forms of nitrogen. In addition it is toxic to aquatic life at certain concentrations dependent on water temperature, salinity and pH. Background concentrations of ammonium are around 15 μg/l (as N) (Meybeck, 1982, quoted in EEA, 1999).

BOD is a key indicator of the oxygenation status of water bodies. BOD is the oxygen demand brought about by organisms in water and sediment acting on oxidisable organic matter. In most European countries the BOD5 test is used where oxygen consumption is measured after five days incubation under controlled conditions. In other, mainly Northern Europe countries, the BOD7 test is used where samples are incubated for seven days. High BOD is usually a result of organic pollution, caused by discharges from wastewater treatment plants, industrial effluents and agricultural run-off. High BOD has several effects on the aquatic environment including reducing river water chemical and biological quality, reducing biodiversity of aquatic communities and reducing the microbiological quality of waters. Background levels are difficult to quantify and are likely to be at or below the detection limit of the analytical method used i.e. between 1 and 2 mg O2/l.

Large inputs of nitrogen and phosphorus to water bodies can lead to eutrophication causing ecological changes that result in a loss of plant and animal species (reduction in biodiversity and ecological status), and have negative impacts on the use of water for human consumption and other purposes.

There are a number of EU Directives aimed at reducing the loads and impacts of organic matter. These include:

  • Nitrates Directive (91/676/EEC).
  • Urban Waste Water Treatment Directive (91/71/EEC).
  • Integrated Pollution Prevention and Control Directive (96/61/EEC).
  • Water Framework Directive.
  • Drinking Water Directive (98/83/EC)

Relation of the indicator to the focal area

Ammonium, BOD, and N and P concentrations indicate water quality. If concentrations are high, quality goes down, threatening aquatic biodiversity and reducing the integrity of the ecosystem and its capacity to deliver ecosystem services.

Enrichment of water bodies with organic matter can lead to oxygen depletion and changes in the trophic structure and functioning of aquatic ecosystems. Until the WFD establishes reference conditions and good status for water bodies -- including, for water bodies impacted by organic matter discharges, type-specific concentrations equivalent to good ecological status, it will not be possible to relate the indicator to specific impacts on ecological status or biodiversity. However, with decreasing concentrations of oxygen consuming substances and nutrient concentrations it can be assumed in general that the water quality of water bodies is improving and by association aquatic life will benefit.

Groundwater is also important as it can be a source of nitrate in rivers adversely affecting associated river and lake water bodies, wetlands and dependent terrestrial ecosystems. Groundwater is also a very important source of drinking water in many countries, and hence it is important to protect its quality also from a human health perspective.


No targets have been specified

Related policy documents

No related policy documents have been specified


Methodology for indicator calculation

The data in Waterbase are collected through the Eionet-Water process and are therefore sub-samples of national data assembled for the purpose of providing comparable indicators of pressures, state and impact of waters on a Europe-wide scale and the data sets are not intended for assessing compliance with any European Directive or any other legal instrument.

Detailed description of the methodology can be found in the specification sheets for EEA core set indicator 019 'Oxygen consuming substances in Rivers'  ( and 020 'Nutrients in freshwater'  (

Methodology for gap filling

No methodology for gap filling has been specified. Probably this info has been added together with indicator calculation.

Methodology references

No methodology references available.

Data specifications

EEA data references

External data references

Data sources in latest figures


Methodology uncertainty

No uncertainty has been specified

Data sets uncertainty

No uncertainty has been specified

Rationale uncertainty


  • The main disadvantage is that the indicator is at present not directly related to effects on aquatic ecosystems: this should improve when WFD assessments are fully implemented (see below for more details).
  • The current selection of stations for Eionet-Water is for assessments at the country level, and representative assessments of individual catchments may not necessarily be obtained. This is being improved as part of the WISE process and development. Information on specific (but not all) water bodies can however be obtained.
  • Another disadvantage of indicators focussing on assessing the water quality (oxygen demand) may be different uses throughout Europe. Some countries use indexes on species level, others on family level. The intercalibration exercise of the EU Joint Research Centre on newly developed assessment systems in Europe to fulfil the requirements of the WFD have recently generated some 'Intercalibration Metrics' that are being widely used throughout Europe to compare country-specific assessment results. See, e.g., Birk and Hering (2006) and Birk et al. (2006).


The indicator has been adopted as an EEA core set indicator. The information basis for the indicator and the assessments possible will improve in time as the WFD assessments are implemented by Member States.

This indicator was selected for the Headline Indicator instead of other globally available indicators (e.g. as used in UNEP GEMS/water), because the EEA core set indicators contain detailed data for a substantial number of European countries.

Further work

Short term work

Work specified here requires to be completed within 1 year from now.

Long term work

Work specified here will require more than 1 year (from now) to be completed.

Work description

SUGGESTIONS FOR IMPROVEMENT This indicator will be improved as more countries implement Eionet-Water. More time series data would improve the data set particularly if from Southern countries. There are gaps in river characteristic information from some countries. Also many countries did not report all the requested summary statistics such as the median. Fill gaps related to catchment pressures. Some countries have used Corine land cover data to provide proxy indicators of pressures. It is expected that this aspect will improve significantly during the next year as new updated Corine data will be available, and as work is undertaken by the ETC/WTR and ETC/LUSI to fill in the gaps in the pressure indicators. Countries will also be designing and/or modifying their monitoring programmes for rivers, lakes and groundwater bodies over the coming years as a requirement of the WFD. This should increase the extent of information potentially available to the EEA through the Eionet‑Water process which will be integrated and extended into the Water Information System for Europe (WISE).

Resource needs

No resource needs have been specified


Not started


2099/01/01 00:00:00 GMT+1

General metadata

Responsibility and ownership

EEA Contact Info

Katarzyna Biala


European Environment Agency (EEA)


Indicator code
SEBI 016
Version id: 1
Primary theme: Biodiversity Biodiversity


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DPSIR: Pressure
Typology: N/A

Geographic coverage


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