Lake Pääjärvi

Pääjärvi is a mesohumic, oligotrophic lake in Finland's southern boreal region. The lake has been extensive monitored since 1970, and sporadically prior to this. The oldest data from the area is in the form of optical properties (Witting 1914), phytoplankton (Levander and Wuorentaus 1917) and a limnological description of the lake was published in 1929 (Järnefelt). The lake water level has been lowered and controlled since 1960. The lake surface area is 13.4 km2 with an average depth of 14.8 m and a maximum depth of 85 m.

University of Helsinki's Lammi Biological Station is located on the Northwest shore of the lake.