Freshwater snails such as Elimia virginica are important grazers in lotic systems. E. virginica is widely distributed, inhabits both high velocity streams and wide tidal rivers and is regularly infected by trematode parasites. Other freshwater snails have shown morphological differences associated with both different flow environments and trematode infection. Additionally, differences in shell morphology and infection have the potential to influence how resistant snails are to high flow disturbance. However, both population variation and response to disturbance are understudied in this species. This study compares population structure, shell morphology and parasite prevalence of E virginica between fast flow (Rappahannock River) and tidal (Potomac River) populations and how those factors influence resistance to dislodgement. To quantify differences in populations snails were randomly sampled (Surber quadrats) at multiplication locations in each river, and preserved in ethanol. Shell width, aperture width and aperture length were measured. Snails were then sexed and dissected for presence of parasites. To measure snails' response to high flow, approximately 300 live snails were collected per river and were subjected to a high flow environment (0.7 m/s) for 10 minutes to determine time of dislodgment. Preliminary results show that sex ratios differed between the sites with females being more abundant in the Potomac. Parasite prevalence didn’t differ between rivers, but males were more frequently parasitized in the Potomac than females. Snails from the Potomac, females and infected snails were wider with larger apertures than Rappahannock snails, males and uninfected snails, respectively. Sex and aperture area were the best predictors of time to dislodgement but the overall model fit was low ( R2 = 0.10). These results illustrate the variable nature of Elimia virginica populations in sex ratio and morphology. However more research needs to be done to better understand factors affecting snail dislodgement in flow.