Regular measurements across the north-south profile of Lake Biwa were performed by a fine scale profiler monthly from April 1994 to March 1995. In the period of extremely low precipitation
when strong stratification appeared
peak value of chlorophyll-a didn’t appear in the epilimnion as usual
rather than
a very sharp chlorophyll peak emerged uniformly in the upper metalimnion of the whole lake. A low dissolved oxygen and high turbidity bottom boundary layer was also observed in the deepest area during summer and autumn. The coincidence between the peaks of Chlorophyll-a and dissolved oxygen shows that the metalimnion is a photosynthesis active region.