The Yangtze is the longest river in Asia, and the longest in the world that flows through a single country. It extends 3,900 miles from glaciers on the Tibetan Plateau to its mouth at the East China Sea, draining a fifth of China’s land mass, which is occupied by a third of China’s population. The tributary Huangpu River runs directly through the megalopolis of Shanghai. Between the mouth of the Huangpu and the Yellow Sea lies an archipelago of islands, the largest of which are Changxing and Hengsha. These are alluvial islands and are enhanced by manmade extensions. The 5.5-mile Yangtze River Tunnel connects Changxing Island with Pudong in Shanghai.