This month, a hundred years after the completion of the Panama Canal, China is expected to finish the first phase of its gigantic South-North Water Transfer Project, known in Chinese as Nanshui beidiao gongcheng — literally, “to divert southern water north.” The phrase evokes the suggestion, attributed to Mao, that “since the south has a great deal of water, and the north very little, we should borrow some of it.”

In realizing Mao’s dream of moving huge quantities of water from areas of plenty to those of want, Beijing is building a modern marvel, this century’s equivalent of the Panama Canal. But whereas the canal inaugurated a century of faith in the ability of human ingenuity to reshape the natural world, the South-North Water Transfer Project is a testament to the limits of engineering solutions to problems of basic environmental scarcity.

China is one of the most water-rich countries in the world. But as Mao observed, its water resources are unevenly distributed and overwhelmingly concentrated in the south and far west. Water scarcity has always been a problem for northern China, but shortages have reached crisis levels as a result of rapid economic development.

For most of the 1990s, northern China’s major river, the Yellow, failed to reach the sea, and the water tables around Beijing and other major northern cities have dropped so low that existing wells cannot tap them. In response, the government has tried to promote water conservation and limit water use. But these measures have had little impact, and there simply isn’t enough water to satisfy growing demands for drinking water, irrigation, energy production and other uses.