Physical map of Jiangsu, China
Physically Jiangsu is flat, with plains covering 68 percent of its total area (water covers another 18 percent). Most of the province stands not more than 50 metres above sea level. Jiangsu also has a well-developed irrigation system, which earned it (especially the southern half) the moniker of (shuǐxiāng "land of water"). The southern city of Suzhou has so many canals that it has been dubbed "Venice of the East" or the "Venice of the Orient". The Grand Canal of China cuts through Jiangsu from north to south, crossing all the east-west river systems. Jiangsu also borders the Yellow Sea. The Yangtze River, the longest river of China, cuts through the province in the south and reaches the East China Sea, which divides the region into two parts: more urban, prosperous south and more poorer, rural north, and these two parts has a tense division. Mount Yuntai, near the city of Lianyungang, is the highest point in Jiangsu, at an altitude of 625 metres above sea level. Large lakes in Jiangsu include Lake Tai (the largest), Lake Hongze, Lake Gaoyou, Lake Luoma, and Lake Yangcheng.
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.