Red tide occurrences and hypoxia are the problems in the worldwide sea and lakes but they are not settled. These phenomena bring about a diminution of fishery significantly. Red tides and hypoxia are considered to be induced by eutrophication. The soluble and particle nutrient compounds that contain nitrogen and phosphorus are considered to induce such eutrophication. But the number of red tide occurrences per year in Japanese bays fluctuates significantly in these 40 years in spite of cutting nutrients from the basin by developing sewage treatment. Are there any other considerable factors...