Abstract
In general, red tide indicates a visual and customary name for the "phenomenon that microalgae in seawater proliferate abnormally, causing a sudden change in sea surface color." However, this is not sufficient to quantitatively understand red tide, and the definition of red tide is not clear. On the other hand, the Ise Bay is considered to have eutrophication and red tide is regularly observed in the Bay. Although the load of nutrient salts has been decreasing, the Bay is one of the areas where determining the relation between red tide and water quality control is difficult. In this study, the author established the criteria to define red tide (red tide index), applied a stepwise method to a multiple regression model, and determined a stable model that has Chl-a (red tide index) as its explanatory variable. Environmental influence was captured by the change in the coefficient of determination of the red tide index model, which implicitly indicated the influence of the Fifth Regulation of Total Pollutant Load Control.
