Abstract
Reservoirs are important infrastructure in that they occupy a major fraction of water resources in our society. Therefore, to study on relationship between catchment conditions and the water quality of rivers is highly required to conduct proper management of the basins. In this study, 65 reservoirs were chosen for the study from all over Japan. Regression analysis revealed that the mean concentration of total phosphorus is expressed by population density and land coverage for agriculture, with a high correlation coefficient of 0.77. Moreover, Projection of water quality during this century was conducted considering population change in the future. Total phosphorus concentration is generally predicted to decrease in the future according to anticipated decline of population in Japan.
