Behaviors of effulent are observed and discussed with reference to the tide and freshwater discharge in the estuary of Suyoung Bay. The esturine front is located at $0.5{sim}1.3km$ seaward from of the Suyoung Bridge at the spring tide, and $0.8{sim}1.0km$ at the neap tide. After the heavy precipitations, the front moved seaward and was located at $1.3{sim}2.5km$ southeast of the Suyoung Bridge. Internal Froude numbers in the estuarine salinity front are estimated approximately to be 1 both at the spring and neap tide. Entrainment coefficient decreases down stream to the estuarine front, and then increases seaward from the estuarine front due to the tidal mixing.