We have developed the survey system for wedge-like saline layer formation and preliminarily checked the resolution of underwater acoustic records in Lakes Nakaumi and Shinji (Coastal lagoons) and Ohashi River. This survey system, which automatically provides a time-series of echo-sounding profiles, is different from the conventional type equipped on a boat. The transducer is fixed on the lake bottom. The echo-sounding record obtained by the new system is clear enough to distinguish the 5%o. halocline. Wedge-like saline layers have distinctly been observed at I .0-1.5m above the lake bottom in Lake Nakaumi.