Published : 22/12/2025
Where is the longest underground river in China? It is located in the deserts of Xinjiang.
The Karez system in Turpan is a man-made underground canal, historically referred to in China as a "well channel". Its underground sections stretch for 5,000 km and are hailed as the "Underground Great Wall".
Recognised as the most mysterious hydraulic engineering project in Chinese history, it has a history spanning over 2,000 years and continues to play a vital role in agricultural irrigation today.
The most mysterious water conservancy project in Chinese history
Turpan (吐魯番) is one of the driest regions in China, with extreme high temperatures of nearly 50°C. The multi-year average precipitation is only about 16 millimetres, whereas Hong Kong's rainfall in 2020 was 2,395 millimetres, showing just how little rain the area receives.
However, this arid place has large oases and is even known as the "paradise of fruits", famed for its production of grapes, Hami melons, and more. The "magic weapon" that turns the desert into an oasis is the Karez (坎兒井).
The Karez, along with the Great Wall and the Beijing-Hangzhou Grand Canal, are known as the three major projects in Chinese history. It is composed of vertical shafts, underground channels, surface channels, and small reservoirs.
The builders dug vertical shafts of varying depths at certain intervals. Utilising the slope of the terrain, they gathered the rainwater, glacial water, and snowmelt that had seeped underground.
They then built underground channels to connect the vertical shafts, diverting the groundwater to areas needing irrigation, where it entered open surface channels. Reservoirs were then built to store water for public use.
The underground channels, located beneath the ground, prevent the water source from evaporating due to the local high temperatures, resulting in extremely high water resource utilisation.
Xinjiang's Karez system has a history of over 2,000 years. During its heyday, there were over 1,700 underground channels. To this day, it continues to benefit the local people, with about 1,200 Karez wells still containing water. The total length of the underground channels exceeding 5,000 kilometres.
Today, the Karez is not only an important water conservancy project but has also become a popular local tourist attraction. In 2006, the "Karez Underground Water Conservancy Project" was listed as a Major Historical and Cultural Site Protected at the National Level.