The Tung-ting Lake, situated at the center of the Middle Yangtze Basin, is the largest fresh water lake in China. It measures 150 km. from east to west and a little less than 100 km. from north to south, with an area of 3,100 sq. km. at the normal flood water level. During the winter, when the water is low, numerous shoals 'and bars appear in the lake, subdividing it into hundreds of small lakes, among which the East Lake and the West Lake are the largest, having an area of 2,106 sq. km. and 394 sq. km. respectively. (Fig. 1) The lake forms an outlet for numerous rivers coming from south and south- west and is connected with the Yangtze by four inlets in its north-western part. The mean annual inflow into the lake is 13,816 cubic meters per second, a little over half of which is furnished by the Yangtze. The lake flows into the Yangtze by one outlet near the city of Yo-yang.