Indicator Assessment

Freshwater quality

Indicator Assessment
Prod-ID: IND-154-en
  Also known as: SEBI 016
Published 21 May 2010 Last modified 11 May 2021
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Pollution of rivers with organic matter and ammonium is decreasing as are the levels of other anthropogenic nutrients in freshwater generally (rivers, lakes and groundwater). This reduces stress on freshwater biodiversity and improves ecological status.

Biochemical Oxygen Demand (BOD5) and total ammonium concentrations in rivers between 1992 and 2006

Note: Between 1992 and 2006, BOD5 decreased from 5 to 2 mg O2/l

Data source:

Waterbase Version 7

Concentrations of nitrate (left, NO3) and phosphorus (right, OP (orthophosphate) or TP (total phosphorus)) in European freshwater bodies in the period 1992-2005.

Note: Concentrations are expressed as annual mean concentrations for groundwater, and station weighted mean of annual mean concentrations for rivers and lakes

Data source:

Waterbase (Version 6)

Biochemical Oxygen Demand (BOD) and total ammonium concentration have decreased in European rivers over the period 1992 - 2005, corresponding to the general improvement in wastewater treatment. BOD and ammonium concentrations are generally highest in eastern, southern and south-eastern European rivers. The largest declines in BOD are evident in the rivers of western Europe, while the biggest drops in ammonium are apparent in eastern European countries.

Concentrations of BOD and ammonium are key indicators of the organic matter and oxygen content of water bodies. They normally increase as a result of organic pollution due to discharges from waste water treatment plants, industrial effluent and agricultural run-off. Severe organic pollution may lead to rapid de-oxygenation of river water along with increased ammonium levels and the consequent disappearance of fish and aquatic invertebrates.

The most important sources of organic waste load are household waste water, discharges from industries such as paper production or food processing and occasional silage or slurry effluents from agriculture. Increased industrial and agricultural production, coupled with a greater percentage of the population being connected to sewerage systems, initially resulted in increased discharge of organic waste into surface water across most European countries after the 1940s. Over the past 15 to 30 years, however, the biological treatment of waste water has increased and organic discharges have consequently decreased throughout Europe.

Nutrient levels in freshwaters are decreasing. The average nitrate concentration in European rivers has decreased approximately 10 % since 1998, from 2.8 to 2.5 mg N/l, reflecting the effect of measures toreduce agricultural inputs of nitrate. Nitrate levels in lakes are in general much lower than in rivers but there has also been a 15 % reduction of the average concentration in lakes.

Agriculture is the largest contributor of nitrogen pollution. Due to the EU Nitrate Directive and national measures the nitrogen pollution from agriculture has, however, been reduced in some regions during the last 10 - 15 years. European air emissions of nitrogen oxides have gone down by one-third over the last 15 years and the deposition of nitrogen on inland surface waters has also declined.

Phosphorus concentrations in European rivers and lakes generally decreased during the last 14 years, reflecting the general improvement in wastewatertreatment and reduced phosphate content of detergents over this period. In many rivers the reduction started in the 1980s. During the past few decades there has also been a gradual fall in phosphorus concentrations in many European lakes. The decrease is due to nutrient removal measures introduced by national and European legislation particularly the Urban Waste Water Treatment Directive. As treatment of urban wastewater has improved and many waste water outlets have been diverted away from lakes, point-source pollution is gradually becoming less important. Agricultura linputs of phosphorus are still significant and need increased attention to achieve a good status in lakes and rivers.

Improving groundwater quality is also important as it can be a source of nitrate in rivers thereby adversely affecting associated river systems, lakes, wetlands and dependent terrestrial ecosystems. At the European level, annual mean nitrate concentrations in groundwater have remained relatively stable since the mid-1990s following an increase during the first half of the 1990s.


EEA Core Set indicators

Supporting information

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.

3. Ecological status of river and lake water bodies.


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

The annual average BOD after five or seven days incubation (BOD5/BOD7) is expressed in mg O2/l and the annual average total ammonium concentration is expressed in micrograms N/l.

The ecological status or potential is presented as a percentage of the total classified water bodies by count.


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 runoff. A high BOD has several effects on the aquatic environment including reducing river water chemical and biological quality, reducing the 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)


Ecological status and potential, as reported in the first river basin management plans, are related to the Water Framework Directive (WFD). The WFD came into force on 22 December 2000, and according to the directive, the first river basin management plans should be published, at the latest, nine years after the directive entered into force. There are, however, serious delays in some parts of the EU and in some Member States consultations are still on-going.

The indicator is directly linked to the objective of the WFD. The main objective of the WFD states that all surface waters should be in good or high ecological status or potential by 2015, or 15 years after entry into force of the directive. The indicator shows the number of water bodies where management measures are needed, and for which water categories and in which regions the need for measures is highest.

Relation of the indicators to freshwater quality and quality of ecosystems

Ammonium, BOD, 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.



The indicator is not directly related to a specific policy target but shows the efficiency of wastewater treatment (see CSI024). The environmental quality of surface waters with respect to organic pollution and ammonium and the reduction of the loads and impacts of these pollutants are, however, objectives of several directives, including the Surface Water for Drinking Directive (75/440/EEC), which sets standards for the BOD and ammonium content of drinking water, as well as other directives mentioned in the previous chapter.

Related policy documents



Methodology for indicator calculation

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

A detailed description of the methodology can be found in the specification sheets for EEA core set indicators 019 'Oxygen consuming substances in Rivers'  ( and 020 'Nutrients in freshwater'  (, as well as in:

Methodology for gap filling

see 'Methodology for indicator calculation'

Methodology references

No methodology references available.



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 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 focusing on assessing the water quality (oxygen demand) may be their different uses throughout Europe. Some countries use species indices, others family indices. The intercalibration exercise of the EU Joint Research Centre on newly developed assessment systems in Europe to fulfill 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).



This 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.

Data sources

Other info

DPSIR: Pressure
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)
Indicator codes
  • SEBI 016
Frequency of updates
Updates are scheduled once per year
EEA Contact Info


Geographic coverage

Temporal coverage



Filed under:
Filed under: water, biodiversity, csi
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