2025 Volume 27 Issue 2 Pages 109-118
The Kanogawa River runs from Amagi Mountains in the middle of Izu Peninsula toward to the foot of Mt. Fuji and discharges into Suruga Bay. The length of the river is 46 km, and the annual mean rainfall of the catchment scale amounts to 2,830 mm at the Yugashima observation site. The quality of river water was examined using public data sources spanning the nearly 30 years from 1990 to 2019. A decrease in organic compound pollution was shown by an apparent change in BOD concentration for all the examined observation points from upstream to downstream. The concentrations of COD and SS also supported this tendency. Other examined parameters such as pH and DO did not support this decrease and they likely came from biogeochemical activities in the river water. The reason for the improvement of water quality can be ascribable to the development of sewage treatment systems in the mid- and downstream catchment throughout the examined 30 years.
