1. Emerging diseases in marine and terrestrial systems have been the subject of several high-profile syntheses but there are no such overviews of emerging diseases in fresh waters. The distinct differences associated with fresh waters merit the separate consideration given to freshwater emerging diseases in this Special Issue.
2. Unique aspects of freshwater environments that can be expected to influence disease emergence include the following: the extreme levels of environmental degradation, overfishing and biodiversity loss arising from preferential human settlement near freshwater bodies for millenia; their relatively small volume and the attraction of animal aggregations that promote disease transmission; and their role as arteries linking terrestrial and marine environments.
3. Understanding emerging diseases entails addressing the multiple drivers that influence the dynamics of host–parasite interactions in a changing world. Structural and functional transformations of ecosystems caused by overfishing may act as an important underlying driver.
4. Climate change may promote disease emergence, but environmental change may cause some diseases to diminish as a result of changes in distributions and abundances of hosts and disease agents. Furthermore, rapid evolution may constrain disease emergence despite environmental change.
5. Appreciating that parasites and pathogens are functional components of healthy ecosystems and that their dynamics may even portend ecosystem change would foster a more complete and balanced view of the value of biodiversity and the ecological role of disease.
6. A multidisciplinary approach will enable a better understanding of disease ecology in general and of freshwater emerging diseases as manifestations of host–parasite interactions to a specific range of conditions.