Populations of hydrobiid snails and their larval trematode parasites in salt marsh along the Skidaway River were studied to determine their distribution. Additionally, the prevalence of larval trematodes infecting the snails was examined to investigate definitive host distribution patterns on the Skidaway River and to identify sites for future studies on second intermediate host susceptibility to trematode infection. To do so, surface sediment and vegetation were collected at low tide from 0.5-m2 quadrats along 20 vertical transects beginning in high marsh at the forest edge and salt meadow, passing through high, medium, and low Spartina alterniflora zones, and ending in the low marsh at creekbed level. Samples were filtered through sieves to concentrate snails, which were then counted and identified. Two species of hydrobiid snails, Spurwinkia salsa (4201 specimens) and Onobops jacksoni (136 specimens) were collected. Hydrobiid snails were found in sediments and on plant stems throughout the S. alterniflora zones, and snail density was greatest in the higher Spartina zones. Sediments from the 3 Spartina zones differed with respect to percent sand, but not percent silt or clay. Salinity and chlorophyll-a levels did not differ between the 3 Spartina zones, and there was no relationship between hydrobiid abundance and the abundance of other snail species. The mean prevalence of trematode infection in S. salsa and O. jacksoni snails was 5.5% and 7.5%, respectively. Snails were infected most commonly with either an oculate monostome, possibly the heterophyid Phagicola diminuta, or 2 types of xiphidiocercariae, one of which likely includes the microphallid Microphallus turgidus. No infected snails were found in over half of the collection sites, and the distribution of infected snails was patchy and unpredictable.