A series of echo-sounding and current measurements as well as the drogue and drift bottle experiments were carried out in the mouth of the Nakdong river from April 1986 to August 1987: Several sand bars and sea channels are formed by reclaiming and dredging work in the river. The main stream of the river is separated into east and west branch channel. The tidal current speed of the west channel is faster than of the east channel in 1986, but is reverse in 1987 to that in 1986.