As a result of climate change, the water temperature of many lakes has risen in recent decades. A further increase is expected. The warming affects the mixing dynamics and thus the oxygen content in the deeper layers of the lakes. Since 2025, data has been collected at various Swiss lakes for long-term monitoring of water temperature and other parameters, measured continuously at both federal and cantonal levels.
Lake temperatures have risen in recent years due to climate change. Since 1980, the surface water in most lakes has warmed by about 0.4 °C per decade. The warming of the deep water is more variable and mostly ranges between 0.0 and 0.2 °C per decade in the deep lakes.
Temperature rise continues
Researchers have modelled the future development of temperature and stratification regimes for 30 lakes in the project Hydro-CH2018. A further increase in the temperature of the surface water layer (down to 1 m deep) is expected in all the lakes: for a scenario without climate change mitigation of between 3 and 4°C in most lakes towards the end of the century.
Effects on aquatic life
Warming has a direct effect on mixing dynamics and thus on the oxygen content in the deeper layers of the lakes. The warmer water causes the stable stratification of the lakes to begin earlier in spring and to dissipate later in autumn. Accordingly, more time is available for the oxygen in the deep water to dissipate. In addition, due to the decreasing intensity or frequency of mixing in some lakes, less oxygen is supplied to the deep water. The changed mixing dynamics also influence the nutrient cycle. As a result, the habitat for fish is restricted and potentially toxic algal blooms can occur more frequently.
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.
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), part of the ETH Domain, was commissioned to install three temperature monitoring stations in the lakes of Murten, Hallwil and Aegeri, as well as in various small lakes, starting in 2021.
Based on the positive results of the pilot project, the following lakes were incorporated into a long-term monitoring programme in 2025, together with the cantons of AG, BE, FR, TI and ZG:
- Large lakes: Lake Murten, Lake Hallwil, Lake Aegeri and Lake Lugano
- Small lakes: Lago Nero, Inkwilersee and Stockseewli
The results of the lake measurements and any adjustments or developments are published on an ongoing basis. In addition, an annual meeting is held with the cantons concerned, Eawag and the federal government, which is coordinated by the FOEN (steering committee). Eawag is responsible for maintenance, data processing, data transfer and scientific monitoring.
© BAFU
Water temperature of selected lakes
Water temperature of Lake Murten
Measurements since July 2022 as part of the FOEN pilot project on lake water temperature, in cooperation with Eawag and the cantonal offices.
Eawag: Temperature Monitoring Lake Murten
with download option of the graphic and data
Water temperature of Lake Hallwil
Measurements since September 2022 as part of the FOEN pilot project on lake water temperature, in cooperation with Eawag and the cantonal offices.
Eawag: Temperature monitoring Lake Hallwil
with download option of the graphic and data
Water temperature of Lake Aegeri
Measurements since November 2022 as part of the FOEN pilot project on lake water temperature, in cooperation with Eawag and the cantonal offices.
Eawag: Temperature monitoring Lake Aegeri
with download option of the graphic and data
Water temperature Lac de Joux
Eawag measurements since 2014.
Eawag: Temperature Monitoring Lac de Joux
with download option of the graphic and data
Water temperature of Lake Geneva
Measurements of the LéXPLORE platform since 2020.
Eawag: Temperature Monitoring Lake Geneva (LéXPLORE Temperature Chain)
with download option of the graphic and data
The indicated base temperature for Lake Geneva is the temperature at 90 m depth at the point where the LéXPLORE platform is located. This is not the deepest point in the lake.
Water temperature Geistsee
Eawag measurements since April 2021, as part of the FOEN pilot project Temperature Monitoring in Small Lakes.
Eawag: Temperature monitoring Geistsee
with download option of the graphic and data
Links
Documents
Swiss lake temperature monitoring program (PDF, 2 MB, 01.02.2019)Commissioned by the FOEN
Last modification 10.03.2025
