There has been remarkable improvement of water pollution conditions of these days, compared to that of the nineteen-seventies. But from the view point of water usage, especially for drinking water, the eutrophication is still a major problem in rivers and lakes. One of the major reason of eutrophication to occur is the excessive loading of nutrients and organic substances to the water body by industrial wastewater and/or household discharge where sewage treatment systems are not sufficient.
The Abukuma River is a very important water resource for use such as drinking water, industrial water, waterpower generation and agriculture in Fukusima prefecture. The water quality of river has been deteriorating and resulting in problems such as water pollution, increasing eutrophication and decreasing of water clarity.
At present, the average concentration of algae flowing into the Abukuma river locality is about 28μg/l. The reason of this high algae concentration was investigated. A number of effluent samples from ponds which are situated within the river basin are regularly examined.
In this report we studied the effect of effluents from fish breeding ponds on eutrophication of the Abukuma river. We want to propose the ways to improve the water qualities and to keep good condition of the Abukuma river as water resouces.

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