Abstract
Kojima Lake, Okayama prefecture, is an artificial lake which was separated from Kojima Bay for the purpose of agricultural water use. Since the separation, the water quality has deteriorated. Therefore, much money has been spent on coutermeasures against the water pollution. By the way, Kojima Lake was needed to feed water for irrigation because rice paddy fields around Kojima lake had been reclamated without preparing enough water for irrigation since 18th century. We investigated the impacts of the reclamation and separation on the water environment and the community around the lake based on the historical data. The reclamation and separation greatly influenced on the water environment and fishery. Most of the short term purposes of the works were attained. But new problems occurred after the completion of the works or some of the purposes became meaningless because of the change of social background.
