The invasive faucet snail (Bithynia tentaculata) has been implicated in massive waterfowl mortality in the Upper Mississippi River Region (UMRR) for the past two decades.The cause of these die-offs is infection by digenean trematode parasites, for which the faucet snail acts as the first and second intermediate host. The trematodes complete their life cycle in migrating waterfowl, where adult trematodes reproduce in the avian gut and can cause fatal hemorrhaging. My first chapter is the compilation and examination of a waterfowl mortality database using observations gathered between 2003-2013 in the UMRR by employees of the LaCrosse District of the Upper Mississippi River National Wildlife and Fish Refuge. We found that mortality was dominated by two species of waterfowl, Lesser scaup and American coot, in a pattern consistent with their relative abundances during migration periods. My second chapter is a field study of trematode infection patterns in faucet snails collected from the UMRR and Oneida Lake (NY), which represent newly invaded and well-established populations of snails,respectively. Over 3,000 snails were necropsied and infection was assessed across multiple years. Substantial geographic, annual, and seasonal variation showed that a number of factors are likely influencing infection patterns in these areas. My third chapter is a lab-based study on the effects of increased temperature and trematode infection on faucet snail mortality and also its effects on trematode development. We exposed faucet snails carrying different stages of trematode infection to increased water temperature. We found that high temperatures have a stronger effect on snail survivorship than infection, but infection also contributes to snail mortality. Additionally, we found evidence that warmer temperatures increase parasite development, though further research is needed to fully investigate this hypothesis. My research provides insight into the biotic and abiotic factors facilitating the invasion of a complex host-parasite system. Furthermore, my research provides critical information to management agencies interested in mitigating negative fitness consequences for migrating waterfowl.