Notable for the large amount of silt it carries, the Yellow River, China’s second longest river, has become a limpid waterway in recent years, thanks to the country’s progress in hydraulic engineering and ecological construction.

Considered both as the cradle of Chinese civilization and the country’s ecological malady, the Yellow River is vital for China’s agriculture, yet the large amount of sediment it carries can clog reservoirs, break levees, and even cause potentially catastrophic floods. According to statistics, if it runs to the sea with sufficient volume, more than 1.1 billion tons of silt can be carried to the sea annually.

Though being rampant with silt for thousands of year, the river has been tamed in the past two decades, thanks to China’s water conservancy projects, including the Xiaolangdi Dam, which have been purging the silt-clogged river since 2002.

“The river has been clean for over ten years, sometimes the color of the river even turns into crystal green. Once a river with great power that can churn up waves as high as 2 meters, it now appears to be quiet and peaceful,” Jia Changzhi, a peasant from Yonghe, Shanxi province, who has been living along the river for his whole life, told the China Youth Daily.

According to experts, ever since the Xiaolangdi Dam started impounding water from the Yellow River in 1999, the slit in the river has reduced significantly. The downstream of the river carried only 64 million tons of silt annually from 2000 to 2015, reducing 1.1 billion from the average since 1950 to 1999.

“The Yellow River has become clean 43 times in history, with the longest clean period of over 20 days in 1727. Since 2000, the river has been clean for even longer periods,” Li Erong, a geological history expert, told the China Youth Daily.

Desludging the Yellow River has always been a dream for many Chinese scientists and the public. Zhu Xianmo, a renowned scientist from the Chinese Academy of Science who died on Oct. 11, has devoted all his life to the cause, pointing out that the permeability of the soil is the key to purge the river.

“If the management of the Yellow River runs smoothly, even elderly people like me may witness emerald water running in the Yellow River,” said Zhu at the age of 88, a dream that has become true as 80 percent of the river remains clean during the non-flood season now.