We propose two types of manipulations. Bottom-up manipulations will affect snail resources, whereas top-down manipulations will affect snail predators. For the bottom-up manipulations, we will clear shistosoma infections in school children, then remove the primary habitat for snails, the submerged macrophyte Ceratophyllum demersum (with proper unmanipulated controls), compost it, apply it to crops, and then quantify reinfection rates and crop yields. The second bottom-up manipulation will be to clear shistosoma infections in school children, apply three agrochemical treatments (status quo control, shift to lower risk herbicides, or eliminate herbicides and fertilizers), and then quantify reinfection rates and crop yields. Farmers will be compensated for any loss in yields. For the top-down manipulations, every village will receive prawns that depredate snails. We will clear shistosoma infections in school children, apply three agrochemical treatments (status quo control, shift to lower risk insecticides that don't kill prawns, or eliminate insecticides), and then quantify reinfection rates and crop yields. Farmers will be compensated for any loss in yields.