The paper is the summary of the investigation studies that author examined for about twenty years in Uranouchi bay where fish culture has been carried out. In the paper environmental characteristics and phenomenon are explained, such as the season of stratification and convection, the intrusion caused by density difference of water between inside of bay and outside of bay, internal tidal wave and estuarine circulation. Finally both environment al improvement methods such as tide dam and enhancing estuarine circulation are proposed.
