Department Surface Waters - Research and Management

The depth of visibility in lakes determines how deep the sunlight penetrates into the lake. This again determines the depth to which the water warms up, and the depth to which algae grow. The depth of visibility in Lake Geneva varies between around 2 and 12 metres. It is measured by sinking a white Secchi disc into the water until it can no longer be seen from the surface. The colour of the disc at half depth represents the so-called Forel-Ule colour.

In early summer 2024, we equipped 300 citizen scientists from the Lake Geneva region with 3D-printed Secchi discs. They were taught how to use a smartphone app with which they can transmit Secchi depths and Forel-Ule colours. Since then, we have been collecting up to 26 measurements a day on our data portal. After just a few months, there were more visibility depth measurements for Lake Geneva than for any other lake in the world. With these measurements, we validate visibility depths derived from satellite data from the Sentinel-3 mission on all cloudless days. 

We promote exchange and collaboration between citizen scientists and participating scientists in joint meetings, in which we discuss the latest measurements from the project. Other current research topics in limnology are also presented with the help of external experts.