On February 1, 1959 the Academy of Sciences of the German Democratic Republic founded the 'Forschungsstelle fUr Limnologie' (now Abteilung Lim- nologie des Zentralinstitutes fUr Mikrobiologie und Experimentelle Therapie der Akademie der Wissenschaften der DDR) in Jena and a research laboratory at Lake Stechlin at Neuglobsow near Rheinsberg used as field experimental station. The foundation followed the building of the first nuclear power plant in the G D R ('Kernkraftwerk I der DDR') in the period 1956-66 between Rheinsberg and Furstenberg (Havel). The nuclear power plant is situated between two stratified lakes - Lake Stechlin and Lake Nehmitz - far from any industrialized area in the midst of extensive woodland. The cooling water is taken from Lake Nehmitz and led away into Lake Stechlin, having passed through the cooling system of the plant. The temperature is on average 10 C above the ordinary level. From Lake Stechlin the water is led back to Lake Nehmitz (Schrader 1962). It was expected that the deep, oligotrophic Lake Stechlin would be loaded thermally and materially by the cooling water circuit, meaning that it would be 'eutrophized', while the slightly eutrophic Lake Nehmitz would be 'oligotrophized'. Thus there would be a solid basis for a research programme on fundamental limnological problems, the solution of which could facilitate problems associated with improvement of conditions in water resources.