The Yangtze or Yangzi is the longest river in Asia, the third-longest in the world and the longest in the world to flow entirely within one country. It rises in the northern part of the Tibetan Plateau and flows 6,300 km (3,900 mi) in a generally easterly direction to the East China Sea. It is the sixth-largest river by discharge volume in the world. Its drainage basin comprises one-fifth of the land area of China, and is home to nearly one-third of the country's population.The Yangtze has played a major role in the history, culture and economy of China. For thousands of years, the river has been used for water, irrigation, sanitation, transportation, industry, boundary-marking and war. The prosperous Yangtze River Delta generates as much as 20% of the PRC's GDP. The Three Gorges Dam on the Yangtze is the largest hydro-electric power station in the world.In mid-2014, the Chinese government announced it was building a multi-tier transport network, comprising railways, roads and airports, to create a new economic belt alongside the river.The Yangtze flows through a wide array of ecosystems and is habitat to several endemic and endangered species including the Chinese alligator, the narrow-ridged finless porpoise, the Chinese paddlefish, the Yangtze river dolphin or baiji, and the Yangtze sturgeon. In recent years, the river has suffered from industrial pollution, plastic pollution,agricultural run-off, siltation, and loss of wetland and lakes, which exacerbates seasonal flooding. Some sections of the river are now protected as nature reserves. A stretch of the upstream Yangtze flowing through deep gorges in western Yunnan is part of the Three Parallel Rivers of Yunnan Protected Areas, a UNESCO World Heritage Site.