Waterborne diseases are the leading cause of mortality in developing countries. The paper emphasize a previously ignored cause of diarrhea - upstream river bathing. Using newly constructed data on upstream-downstream hydrological linkages along with village census panel data in Indonesia, find that upstream river bathing can explain as many as 7.5% of all diarrheal deaths. Results, which are net of avoidance behavior, show no effect of trash disposal on diarrheal infections. Furthermore find that individuals engage in avoidance behavior in response to trash disposal (visible pollutants) but not river bathing (invisible pollutants). It conduct policy simulations to show that targeting upstream individuals could generate substantial environmental and health savings relative to targeting downstream individuals. This provides a potential roadmap for low- and middle-income countries with limited resources for enforcement of water pollution.