Freshwater ecosystems are inherently dynamic, but the scale and frequency of change are increasing under the combined influence of altered flow regimes, drought and flooding, catchment modification, biological invasions, climate change and human-mediated movement of aquatic species. While the consequences for fish populations are increasingly recognised, much less attention is given to their effects on parasites and the ecological relationships required for parasite transmission. This presentation explores how natural and human-driven changes in freshwater ecosystems can alter parasite exposure, transmission and infection in fish, and what these responses may reveal about fish health and ecological connectivity. Using examples relevant to Australian freshwater environments, I will consider several pathways through which ecosystem change can reshape host–parasite relationships. Altered water flows can concentrate or disperse hosts, reconnect previously isolated habitats and change opportunities for transmission. Rainfall, flooding and catchment run-off can connect terrestrial and aquatic environments, introducing parasite stages and other biological material into waterways. Changes in temperature/water quality/food webs and the abundance of intermediate/definitive hosts can disrupt parasite life-cycles or create new transmission opportunities. The introduction/translocation/stocking of fish can further reshape parasite communities through the movement, loss or acquisition of parasites. Importantly, the presence of parasites does not necessarily indicate an unhealthy ecosystem, nor does their absence indicate a healthy one. Parasites with complex life cycles depend on interactions among multiple species and can therefore provide information about trophic relationships, biodiversity and ecological connectivity. At the same time, environmental disturbance may create conditions in which particular infections emerge as significant threats to fish health. Understanding freshwater fish health therefore requires us to look beyond the fish itself. Integrating parasitology with fish biology, catchment processes and ecosystem monitoring can provide a more complete picture of how freshwater systems respond to change and reveal changes that might otherwise remain beneath the surface.