Abstract
The Sada River is a canal, 8.3km in length, built about 200 years ago which connects the Sea of Japan with Lake Shinji directly. Observation was carried out using a automatic water quality and current meter to investigate the movement of invading sea water through the River. The results indicated that, though the movement of the river water is basically controlled by the tidal fluctuation of the Sea of Japan, the sea water can scarcely reach Lake Shiniji because of the long distance of the canal and small tide range of the sea. The acceleration of sea water upstreaming mainly depends on the pushing effect of a strong west wind and sea water swelling due to the low atmospheric pressure in the Sea of Japan. The moment the upstreaming of oxygen-rich sea water into the lake depends on the atmospheric conditions which is inconsistent. If it is possible to control artificially the inflow of sea water into the lake, it will greatly enhance the self-purification of the lake water and bottom sediment which in turn will increase the benthic biological activity.
