the shinkagishi river watershed used to be an area where water quality deteriorated markedly, but in recent years, water quality has been improving due to the construction of a watershed sewerage system and water purification projects. however, water quality has not improved in some upstream areas of tributaries located in the sayama hills. a two-year study was conducted from December 2020 to identify the sources of contamination. based on the survey results, the characteristics of the water environment, particularly water quality, are discussed.