In the regional development, a balance of development and preserving of natural resource should be considered. The precious natural environment has to be maintained. The Lake Ogawara in Aomori Prefecture is one of large brackish lake where the most dominant water organism for fishery is Corbicula japonica. And the water quality and the flow of the lake is very related to the habitation of the clams. The field observation of water quality was carried out for this lake in the period for three years from August 2002. From a viewpoint of water quality environment, egg-l aying and hatching of them are performed on the north side of the lake, and they diffuse throughout the lake by the flow.