800 Li quicksand boundary, 3,000 weak water depth. Goose feathers will not float, but reed flowers will sink.

On the 22nd trip to the West, when Tang Sanzang collected sand monks, there was a poem describing the danger of quicksand river: 800 quicksand boundary, 3,000 weak water depth. What does weak water mean here?

Looking through books, it is generally believed that many shallow rivers can only cross the border by raft, not by boat, because the water is too weak to carry a boat, so such rivers are called weak water, such as Shangshu? Yugong recorded that "weak water leads to stand out from the crowd", Shangshu noted the ancient prose "weak water leads to Zhangye", and Shan Hai Jing recorded that "there is water in the north of Kunlun, hence the name weak water".

However, the combination of weak water and numbers generally refers to danger and distance, such as Gao Tai in Jinshan Temple by Su Shi, Penglai is unreachable, weak water is three Wan Li, Shuilongyin-Looking at Jiuhua Mountain by Xiaoxiang, Zhang Song, Fuzzy Pearl House is silly, Looking at Penglai without weak water, Dream of Red Mansions and so on. The geography book Weak Water is also used to refer to the Poyi River or Heishui River in the northwest. "The Xiongnu of Zhaowucheng, the capital of Yue family, is on the bank of weak water." There is also a weak river on the map of Gansu Province.

But what I want to say is "800 quicksand boundary, 3 thousand weak water depth, goose feathers can't float, reed flowers sink to the bottom."