Long-term changes in the water quality of Lake Biwa

The Shiga Prefecture Fisheries Experiment Station has continuously monitored the water quality and appearance of Lake Biwa (Shiga, Japan) since 1915, in order to gain an understanding of the environment of the lake's fishing grounds. The following phenomena have been observed: 1) transparency began to fall in the 1930s and reached a minimum between the late 1970s and the early 1990s; 2) plankton biomass increased in the 1950s but has been maintained at the same level since the 1960s; 3) both the surface and bottom water temperatures have risen about 1C over the past 20 years; and 4) The concentrations of both surface and bottom nutrients have been rising since the 1960s, and they have been accumulating in Lake Biwa.