The blogger's concern over silt, mainly deposits of mud and sand, appears a little more reasonable, though, because it is unavoidable given the relatively slow flow of water in the Danjiangkou Reservoir in Hubei province, a major source of water for the project. But this problem is confined to the Danjiangkou Reservoir, because the flow of water in the central canal will ensure that it is not plagued by silt. Thus, there is no need to worry about the canal being damaged by silt.

Even the silt in the Danjiangkou reservoir is nothing serious. The reservoir, built in 1958, is a multi-purpose facility that serves as a major source of water for the region, generates electricity and controls floods. Since the canal that supplies water to power plants is situated at a lower altitude than the one which supplies water to the south-north project, silt in the reservoir won't do any harm as long as the hydraulic power plant functions normally.

Silting is a normal phenomenon, typical of all reservoirs. Every reservoir has a balancing point of silt deposits and the volume of water, and the Danjiangkou Reservoir reached that point long ago. The blog posting didn't consider this most basic principle.

According to project authorities, the climate varies along the canal, which stretches 1,432 km from South to North China, and the section north of Anyang in Henan province could freeze in the winter. It is estimated that the rate of flow in the canal would drop by 40 percent because of the freezing on the surface - but that will not affect the flow of water under the surface.

Concern over the South-North project is welcome, but spreading rumors is rather destructive. Once the water from the south reaches Beijing, rumors will die a natural death.

The author is a senior researcher at China Society for Hydropower Engineering.