In 486 BC, King Fuchai of Wu built the Hangou Canal connecting the Huai River and its tributaries, including the Si, to the Yangtze River to the south. Three years later, in 483 and 482 BC, he expanded this network with the Heshui Canal, connecting the Si to the Ji River, creating a waterway system that linked northern and southern China centuries before the Grand Canal formalized these routes. The Si River was not merely a waterway; it was a strategic corridor through which armies and trade goods moved between the competing states of Qi, Jin, and Wu during the Spring and Autumn period. Its tributaries, the Fan, Sui, Tong, and Yi, swelled its banks as it passed through what are now Yutai, Pei, Xuzhou, Suqian, and Siyang counties, making it one of the most important rivers in the ancient Chinese heartland.

In 1194, floods changed the Si River's course, severing its connection to Jiangsu Province. But the real destruction came during the Yellow River floods of 1851 to 1855, when the Yellow River once again shifted its course northward, assuming the path of the former Ji River and passing north of the Shandong Peninsula. The immense quantity of silt the Yellow River carried left behind a layer of mud four meters deep across the Si River's former lower reaches. The river that had once connected the Mengshan Mountains to the Huai River now ends at Lake Nanyang, a remnant of a much larger waterway system. What the Si River lost to the Yellow River's wandering course, it could never reclaim. The silt was too deep, the terrain too altered, the hydrology permanently rearranged.

Beyond its practical significance, the Si River carried mythological weight. Chinese tradition held that the legendary Nine Tripod Cauldrons, symbols of dynastic legitimacy cast by Yu the Great after he tamed the primordial flood, were lost somewhere in the Si River. To lose the Nine Cauldrons was to lose the mandate of heaven itself, and the Si River thus became a place where political power and cosmic order intersected. The river's name was preserved long after its lower course vanished, living on in the imperial Si Prefecture and Subprefecture and in the present-day Si County in Anhui Province. Names outlast rivers, it turns out, just as rivers outlast the kingdoms that depended on them.

The modern Si River rises in the southern foothills of the Mengshan Mountains, flows through Sishui County and the cities of Qufu and Yanzhou, and empties into Lake Nanyang. It is a modest river now, its glory days as a trunk route of ancient Chinese hydrology long past. At Qufu, the Jinkou Dam spans the river where it passes near the tomb of Confucius, a place of pilgrimage for over two thousand years. The philosopher who taught beside this water could not have imagined that the river itself would one day shrink to a fraction of its former reach. But the Si River's diminishment makes its surviving stretch through Qufu feel more precious, a remnant of the ancient world that Confucius inhabited and that his teachings helped define.