The fate of chemicals in a lake environment has a close relationship with hydraulic events. Animate and inanimate as water quality affect one another in the lake. Accordingly, water movement is an important issue for understanding the material cycle and effects of environmental pollutants in the lake.
In this paper, three methods for investigation in Lake Suwa were introduced. First is the continuous observation of water temperature by using temperature logger. And its results showed that the formation and destruction of thermal stratification were repeated in summer season. Second is our routine water quality observation data as Secchi disk transparency. Recently, transparency has improved in summer season, as a result of decrease of phosphorus amount in the lake water. Third is the analysis of dioxins in the sediment. The major source was impurities of chemical herbicides (PCP and CNP). And large amounts of dioxins flowed into the lake in flood stage compared to normal stage.
