The South-to-North Water Diversion Project stands as the largest water redistribution initiative in China’s history. This monumental engineering endeavor comprises three major routes—Eastern, Central, and Western—spanning over 4,000 kilometers and linking the Yangtze, Huaihe, Yellow, and Haihe river basins. With a cumulative investment exceeding 500 billion yuan, it transfers more than 10 billion cubic meters of water annually to the north, equivalent to a quarter of Lake Taihu’s volume. However, the very nature of this transferred water poses a hidden challenge: it is not purified water but natural river water, carrying fish, plankton, algae, microorganisms, and even seeds and eggs of submerged plants.
For instance, the Central Route begins at the Danjiangkou Reservoir, traversing Henan, Hebei, Beijing, and Tianjin before reaching its endpoint at Beijing’s Tuancheng Lake. Throughout this 1,714-kilometer journey, the water encounters almost no effective “filters” to block all organisms. The latest news reveals that at least 10 aquatic species originally native to southern China have been detected in northern water bodies. These include water hyacinth, alligator weed, golden apple snails, Taenioides cirratus, and Tridentiger bifasciatus. A notable example is the golden apple snail, originally from South America. Introduced to China in the 1980s as an edible species, it proliferated rapidly in southern waters. Its eggs have now been found in canals across Hebei, Henan, and even Beijing. These snails not only devour aquatic vegetation and disrupt ecosystems but also carry parasites, threatening human and animal health. Thus, the issue is not the water transfer itself but the unintended creation of a high-speed corridor for biological migration, which continues to operate.
Once invasive species take root, they often overpower native species.
With no natural predators in new environments and high adaptability, invasive species can spread rapidly. Water hyacinth, for example, can grow dozens of leaves daily and reproduce a hundredfold within a year, capable of covering an entire river surface in a month. This blocks sunlight, depletes oxygen, and collapses underwater ecosystems. Native fish, shrimp, and algae in northern waters face shrinking habitats and potential extinction. Moreover, these invaders can alter the chemical balance of water bodies. Blue-green algae, common in southern waters, can trigger algal blooms in northern reservoirs under sunlight, warm temperatures, and eutrophic conditions. This leads to foul-smelling, green water and compromises drinking water safety. The 2007 algal bloom in Lake Taihu, which affected millions of residents in Wuxi, serves as a stark warning. Similar incidents in northern reservoirs along the diversion routes could have magnified consequences, as these reservoirs serve as critical urban water sources.
Once invasive species become established, the cost of control is extremely high, and complete eradication is almost impossible.
The U.S. experience with Asian carp in the Mississippi River exemplifies this: despite over $1 billion spent on electric barriers, water gates, acoustic deterrents, and fishing campaigns, the species persists and has even reached the Great Lakes. Similarly, in Chinese cities like Shenzhen and Guangzhou, efforts to control golden apple snails through trapping, pesticides, dredging, and manual removal have proven costly and inefficient, with frequent resurgence.
Crucially, the South-to-North Water Diversion is not a closed system but a dynamic, cross-basin network. Cleaning one branch canal may be futile, as the main pipeline can continuously introduce new organisms. Thus, proactive source control is more effective than post-invasion. Strategies include biological screening, ecological buffer zones, and advanced filtration systems using ultraviolet light or pressure differentials to intercept organisms. However, these measures increase engineering costs and technical demands. Realistically, halting the project is not an option—it is the lifeline for over 100 million people in regions like Beijing-Tianjin-Hebei, Henan, Shandong, and Anhui. Since its operation began in 2014, the Central Route alone has transferred over 60 billion cubic meters of water, meeting nearly 70% of Beijing’s water needs.
But what we can do is turn this “highway” into a “highway with checkpoints.”
This involves enhanced monitoring at water sources to identify high-risk species early, installing ecological isolation devices (e.g., multi-stage sedimentation tanks, micro-filters, and biological barriers), and creating biological buffer zones in tributaries and lakes along the route to intercept or neutralize species mid-journey. Additionally, an “ecological concomitant management” approach could be adopted: alongside water transfer operations, restoring aquatic ecosystems by planting native vegetation and introducing native filter-feeding fish to build ecological “immunity.” While completely halting species movement is unrealistic, making them unable to adapt can prevent large-scale disruption. This project transfers not just water but potentially the dawn of a new ecological era. How and where we transfer water is not merely an engineering problem but a critical question for the entire biological community.
