Indicator: Change in the concentration of total phosphorus in lakes
Indicator name

Tag: WAT003
Indicator abbreviated name

Definition: Percentage of change in the concentration of total phosphorus in lakes between 2007 and 2023
Definition describing what the indicator measures

Unit: % of change in concentration
Measurement unit of the indicator values

Spatial coverage: EU (national values are available for 20 Member States: Austria, Bulgaria, Cyprus, Germany, Denmark, Estonia, Spain, Finland, France, Croatia, Ireland, Italy, Lithuania, Latvia, Netherlands, Poland, Portugal, Romania, Sweden, Slovenia)
Geographic area covered by the indicator

Temporal coverage: 2007-2023
Time coverage of the indicator from first to most recent available year

Update frequency: Every year
Frequency at which indicator is updated

DPSIR: State
DPSIR classification framework: Driver, Pressure, State, Impact, or Response

Method: The methodology focuses on spatial representativeness by analysing data at the water body (WB) level: 1) annual mean concentrations are calculated per monitoring site. These site time series are then aggregated to WB time series using Generalized Additive Models (GAM), which simultaneously fill gaps in the data. The resulting WB series are averaged into country-level time series; 2) for the final European-level result, country averages are weighted based on the total water size (river length for rivers, area for lakes and groundwater) to avoid bias toward countries with high monitoring density. Countries with very low sampling density are excluded from this step; 3) calculation of the difference in concentration between the year 2007 and the year 2023.
Description of the main methodological steps used to calculate the indicator

Reference: Nutrients in freshwater in Europe - European Environment Agency, (https://www.eea.europa.eu/ims/nutrients-in-freshwater-in-europe), accessed 19 March 2026
Reference sources describing the indicator and method to calculate it (e.g. peer-reviewed articles, scientific/technical reports, webpages, other)

Producer: European Environment Agency
Institution which produces the calculation of the indicator values

Provider: European Environment Agency
Institution supplying the indicator values, even if not the original producer of indicator values

Open source: False
Indicates whether calculation code is openly available

Spatial scope (Member States): True
Whether the indicator is available at Member States level

Spatial scope (EU27): True
Whether the indicator is available at EU27 aggregated level

Spatial scope (global): False
Whether the indicator is available at global level

Accuracy uncertainties: Methodology uncertainty: nutrient conditions vary throughout the year depending on, for example, season and flow conditions. Hence, the annual average concentrations should ideally be based on samples collected throughout the year. Using annual averages representing only part of the year introduces some uncertainty, but it also makes it possible to include more sites, which reduces the uncertainty in spatial coverage. Moreover, the majority of the annual averages represent the whole year. Total phosphorus concentrations in lakes originate mainly from anthropogenic activities as a result of agricultural land use. Concentrations in water are the effect of a multidimensional and time-related process, which varies from water body to water body and is less quantified. To properly evaluate the total phosphorus concentration in lakes and its development, closely-related parameters such as ammonium and dissolved oxygen should be taken into account. Datasets uncertainty: the indicator is meant to give a representative overview of nutrient conditions in European lakes. This means it should reflect the variability in nutrient conditions over space and time. Countries are asked to provide data on important water bodies according to specified criteria. The datasets for lakes include many countries within the EEA, but the time coverage varies from country to country. It is assumed that the data from each country represents the variability in space in their country. Likewise, it is assumed that the sampling frequency is sufficiently high to reflect variability in time. In practice, the representativeness will vary between countries. Each annual update of the indicator is based on the updated set of monitoring sites. This also means that due to changes in the database, including changes in the quality control procedure that excludes or re-includes individual sites or samples and retroactive reporting of data for the past periods, which may re-introduce lost time series that were not used in the recent indicator assessments, the derived results of the assessment vary in comparison to previous assessments. Waterbase contains a large amount of data collected over many years. Ensuring the quality of the data has always been a high priority. Still, suspicious values or time series are sometimes detected and the automatic quality control routines exclude some of the data. Through the communication with the reporting countries, the quality of the database can be further improved. Rationale uncertainty: using annual average values provides an overview of general trends and geographical patterns in line with the aim of the indicator. However, the severity of shorter-term, high-nutrient periods are not reflected.
Comment on data accuracy, limitations, and uncertainty

Comments: None
Additional remarks

Storage

Copyright/Licence of use: See EEA Copyright/Licence Policy: https://www.eea.europa.eu/legal/. The data are provided by EEA based on data reported by the countries.
Copyright or licensing information related to the indicator