Construction of the Xayaburi dam on the Mekong River in Laos could have serious implications for public health as well as for fishing (Nature 478, 305–307; 2011).

The river and its basin are the natural habitat of the freshwater snail Neotricula aperta. This is the only known intermediate host of the trematode parasite Schistosoma mekongi, a flatworm that causes human schistosomiasis (bilharzia) through contact with infected water.

Newly created upstream water reservoirs, as well as altered river currents and sedimentation, markedly affect the relative distribution of snails carrying different Schistosoma species. When the Aswan High Dam was built in Egypt in 1970, it caused a shift in the relative frequency of schistosomiasis from the urinary (S. haematobium) to the hepatosplenic type (S. mansoni), which is more severe (M. F. Abdel-Wahab et al. Lancet 314, 242–244; 1979).

Construction of the Three Gorges Dam across the Yangtze River in China is also expected to extend the snail's normal habitat substantially, increasing the likelihood of disease in domestic livestock and humans (D. P. McManus et al. Clin. Microbiol. Rev. 23, 442–466; 2010).

The only cost-effective drug currently available to treat infection is the schistosomicide praziquantel. However, parasite resistance to this drug is emerging as a result of mass administration programmes and high rates of reinfection in endemic areas (S. D. Melman et al. PLoS Negl. Trop. Dis. 3, e504; 2009).

A plea on behalf of poor people living along the Mekong's banks is unlikely to affect the construction of economically important projects such as the Xayaburi dam. Instead, some of the dam's revenues should be invested in the development of new antischistosomal drugs and vaccines.