The natural reason why Dongting Lake has become the second largest freshwater lake is mainly the siltation of the Yangtze River. From the position, Dongting Lake is close to the upper reaches of the Yangtze River, with fast velocity and much sediment. The lake basin is low in terrain, which is favorable for sediment to enter. There are many water systems connected with the Yangtze River, with a large amount of water entering the lake and receiving more sediment. Poyang Lake is close to the lower reaches of the Yangtze River, with slow water flow, more sediment deposited on the riverbed and less sediment entering the lake. The lake basin is high in terrain, and sediment is not easy to enter. There is only one entrance to the river, so the amount of water entering the lake is small, and the lake receives less sediment. Therefore, Dongting Lake is more susceptible to sediment deposition in the Yangtze River than Poyang Lake.

In addition, the artificial reason why Dongting Lake has become the second largest freshwater lake is the artificial reclamation of the lake. Due to the continuous reclamation of farmland around the lake, the area of cultivated land has expanded, and the flood storage capacity of Dongting Lake has declined.

Dongting Lake is the second largest freshwater lake in China, located in the north of Hunan Province and the south bank of Jingjiang reach of the Yangtze River. It is an important water storage lake in the Yangtze River. Dongting Lake receives water from Songzi, Taiping, ouchi and Diaoxian counties of the Yangtze River, and is connected with Hunan, Guizhou, Yuan and Li in the south and west, and flows into the Yangtze River from Chenglingji, Yueyang City.