The Changjiang River (also called the Yangtze River) is the longest river in China. It originates from the Tuotuo River on the southwestern side of the snow-draped Geladandong—the main peak of Tanggula Mountains of the Qinghai and Tibet plateau; it flows through provinces or autonomous regions of Qinghai, Tibet, Sichuan, Yunnan, Hubei, Hunan, Jiangxi, Anhui and Jiangsu, and finally enters into the East China Sea in Shanghai. It has a length of 6300 kilometers and a catchment area of 1.8 million square kilometers, which equivalent to 1/5 of the total land of China. The main tributaries of the Changjiang River are eight rivers of the Yalongjiang, the Minjiang, the Jialingjiang, the Wujiang, the Xiangjiang, the Yuanjiang, the Hanjiang and the Ganjiang that all have a catchment area of above 80,000 square kilometers. The upper stream of the River is from the source to Yichang with a length of 4510 km. The river passes high mountains and deep valleys with many turbulent. The water head in this section is 5360 m, accounting to 98.9% of the total of the river. The famous "Three Gorges" of 209 km long is just located in this section. From Yichang to the Poyang Lake, the river enters into the middle reaches with a length of 940 km. Down from the Lake mouth of Poyang is the lower reaches of the river with a length of 850 km. From Zhicheng in Hubei Province to Chenglingji - outlet of the Dongting Lake, the river has a high degree of risk of flooding in this section because lowland are scattered along the river. In the middle and lower reaches of the river, many big lakes are connected, namely the Dongting Lake, the Poyang Lake, the Cao Lake and the Tai Lake.