Indicator water

Animal and plant communities in bodies of water are often not near-natural, especially in the densely populated and intensively used areas of the Swiss plateau. This is evident from the biological assessment of streams and rivers. A majority of the surface waters studied cannot sufficiently fulfil their function as habitats.

The biological indices used for the studies react differently to pressures on water. For example, a stretch of surface water with a low nutrient load but high structural deficits is rated 'good' with the diatom index, but 'poor' with the fish and macrophyte index. For this reason, the percentage of surface waters that do not meet the ecological goals varies depending on the bioindicator.

The diatom index shows good to very good water quality at over 90% of the monitoring sites. From this, conclusions can be drawn primarily about the nutrient levels in the bodies of water studied. These have improved greatly since the 1980s, particularly due to the construction of wastewater treatment plants.

The assessment of the biological status of surface waters using fish and aquatic plants as indicators is particularly poor. Both indicators react to a number of different pollutions and are therefore particularly well-suited to depicting the complex interplay and amount of human influence overall. The overall biological status is therefore assessed as poor.

The greatest deficits are in the densely populated and intensively-used Swiss Plateau. The reasons for this are pollution, the lack of diversely-structured habitats and the severe fragmentation of bodies of water by migration obstacles.

To date, only three national monitoring campaigns have been carried out. Over this period, assessments based on biological indicators have remained very similar. Graph "Trend assessment on the basis of fish" shows the development of water status over time based on the fish index, which illustrates the different pressures on water particularly well. Because there is no evidence of significant improvement so far, the trend is classified as unsatisfactory. Due to the short time series, however, this assessment must be viewed with caution.

In order to improve the status of the waters, selected wastewater treatment plants are being upgraded with a treatment stage for micropollutants. Rivers, streams and lakes are being revitalised, more space is being given to bodies of water and the negative impact of hydropower exploitation is being reduced. These measures are having a positive impact on aquatic life and water quality, although these improvements are usually only measurable locally.

• Related indicators
• Nutrients in watercourses

The European Water Framework Directive (WFD, Directive 2000/60/EC) establishes a standardised basis for surface water monitoring in the EU. The member states assess the various quality components using their own national methods according to the requirements in Annex V of the WFD. In order to ensure comparability of the results between the member states, the WFD provides for intercalibration of the national methods. The assessment of Swiss surface waters is carried out using a five-step scale in accordance with the requirements of the WFD, so that the results of surveys in neighbouring countries are comparable with results of surveys in Switzerland at the final classification level.

The invertebrates, diatoms, aquatic plants and fish organism groups are assessed according to five quality classes under the Modular Stepwise Procedure.

The total number of monitoring sites assessed differs depending on the organism group. Invertebrates: 107 monitoring sites; fish: 63 monitoring sites; diatoms: 104 monitoring sites; and aquatic plants: 38 monitoring sites.