Huai River
Before 1194 A.D., the Huai River cut through north Jiangsu to reach the Yellow Sea. The Huai River is a major river in central China, and it was the traditional border between North China and South China. Since 1194 A.D., the Yellow River further to the north changed its course several times, running into the Huai River in north Jiangsu each time instead of its other usual path northwards into Bohai Bay. The silting caused by the Yellow River was so heavy that after its last episode of "hijacking" the Huai River ended in 1855: the Huai River was no longer able to go through its usual path into the sea. Instead it flooded, pooled up (thereby forming and enlarging Lake Hongze and Lake Gaoyou), and flowed southwards through the Grand Canal into the Yangtze. The old path of the Huai River is now marked by a series of irrigation channels, the most significant of which is the North Jiangsu Main Irrigation Canal (), which channels a small amount of the water of the Huai River alongside south of its old path into the sea.