Monitoring network: Water temperature

Temperature is one of the key physical parameters influencing the chemical and, above all, biological processes in a watercourse. The FOEN operates a water temperature monitoring network for watercourses. A federal pilot project for long-term monitoring of lake water temperature runs until 2024.


The temperature of water influences all metabolic processes, the duration, course and speed of growth as well as the composition of the biotic communities that live in it. The viability and activity of aquatic organisms require certain temperature limits and optimum conditions. It is therefore very important to understand how water temperature fluctuates.

The FOEN's temperature monitoring network provides the basis for monitoring the effectiveness of Swiss environment protection legislation (Water Protection Act and Ordinance). It also helps us to understand the factors affecting temperature (e.g. thermal power plants, anthropogenic heat input and withdrawal, water management interventions, climate trends).

The FOEN conducts temperature monitoring in cooperation with cantonal and national specialist and research agencies (cantonal water protection and fisheries agencies, MeteoSwiss, Eawag, etc.).

1. Temperature measurements in watercourses

The FOEN has been operating a temperature monitoring network in watercourses since the 1970s. Care is taken to ensure that the
measurements take on one bank of the river yield representative results for the entire river cross-section. The monitoring network comprises around 80 stations.

The measuring stations are all equipped with temperature probe, transmitter and data logger. Up-to-date data can be viewed on the internet and on various apps or received via SMS. The data and statistical values over the entire measurement period are published in tabular form on the internet. Evaluations of the temperature data are also published in the Hydrological Yearbook.

 

2. Temperature monitoring in waterbodies

Lakes are of great importance for drinking water supply, fisheries, recreation and tourism as well as a habitat for plants and animals. It is therefore important to conduct targeted monitoring to observe temperature changes in Switzerland's lakes. In order to gain an understanding of the effects of climate change, reliable and meaningful monitoring involving long-term measurements with high temporal resolution is required. This is a federal task to complement the monitoring carried out by the cantons. As the existing temperature monitoring networks are insufficient for the purposes of preventive environmental monitoring, the FOEN is extending the federal system to include lakes.

Selected lakes for the FOEN pilot project
Temperature monitoring in Swiss lakes: distribution of Swiss water bodies in relation to their elevation and surface size (small blue dots). Lakes with a size of more than 30 m2 are taken into account. Highlighted are those water bodies (blue circles) where water temperature is continuously measured for the FOEN project. The yellow bars show the summary shares of the water surface of the Swiss lakes: the surface share of the three largest lake groups amounts to 96% of the total lake water surface. The remaining 4% is formed by several thousand smaller lakes, ponds and basins. Despite their smaller size, they are ecologically very important. Therefore, the effects of climate change are also being studied there.

Waterbodies are selected for which trends can be observed on the basis of continuous measurement series. The aim is to create a meaningful and nationwide database as a basis for more reliable model forecasts. Furthermore, measurement techniques at the pilot stations can be evaluated with regard to their reliability and cost.

The following were taken into consideration when selecting the lake monitoring stations:

  • Supplements existing cantonal measurements
  • Inclusion of an oligotrophic lake at a somewhat higher altitude and an eutrophic lake at the Swiss Plateau (different stratification behaviour of the lake, different degree of fouling on the instruments).
  • Small lakes and ponds also considered
  • Possible high sensitivity to climate change
  • Availability of existing monitoring data over a longer period of time
  • Temperature recording in the depth profile at the deepest point of the lake
  • Good accessibility for field work and maintenance

As part of a pilot project funded by the FOEN, the Swiss Federal Institute of Aquatic Science and Technology (Eawag) has been commissioned to set up three temperature monitoring stations in Lakes Murten, Hallwil and Aegeri. They will be commissioned in summer to autumn 2022. Water temperature is also measured continuously at various depths in eight other small lakes.

Wassertemperatur des Hallwilersees

Lake temperatures

State of waterbodies: Watertemperatures of lakes in real time

Image: Temperature of Lake Hallwil in September 2022

Photos

Boje zur Temperaturmessung im Murtensee
Buoy to measure the temperature in Lake Murten
© BAFU
Boje zur Temperaturmessung im Hallwilersee
Buoy to measure the temperature in Lake Hallwil
© BAFU
Boje zur Temperaturmessung im Ägerisee
Buoy to measure the temperature in Lake Aegeri
© BAFU

Further information

Contact
Last modification 11.11.2022

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