The Mondsee Limnological Institute site is a Natura 2000 area in Upper Austria. Connected to the Research Institute for Limnology, Mondsee of the University of Innsbruck this site has a long tradition of data sampling. The LTER Site Mondsee in the Salzkammergut lake district is of high ecological, socio-economic and touristic importance. In the 1960s and 1970s the lake underwent a period of eutrophication, followed by a period of re-oligotrophication due to sewage water treatment in the 1980s. The lake has been monitored since the 1950s, mainly by the Research Institute for Limnology, Mondsee of the University of Innsbruck and the Institute for Water Ecology, Fisheries and Lake Research of the Federal Agency for Water Management. Long-term data sets are available for physico-chemical parameters (temperature, oxygen, pH, conductivity), nutrients, and phytoplankton.