Abstract
The decades-long changes and seasonal variations of water quality in the Kojima Lake, Sasagase River and Kurashiki River were investigated based on water quality observations at public access points. Each of these two rivers flows into the Kojima Lake. As a result, it becomes clear that the improvement of the lake water quality is statistically significant since the year 1995, and that water quality varies yearly at many observation points. In addition, the decades-long changes of the water quality were investigated, taking into account water purification countermeasure such as dredging of lake sediments and reduction of pollution load. comparing with the water purification countermeasure such as dredging of lake sediments and reduction of the pollution load.
