Abstract: In a 12 month study, the ecology of freshwater snails in Opa Reservoir (OR) and Research Farm Ponds (RFPs), in Obafemi Awolowo University, Ile-Ife, Nigeria, was studied. During each monthly visit, eleven sites (seven sites in OR and four sites in RFPs) were sampled for relative snail density, vegetation cover and physicochemical properties of the water bodies. The data were analysed using non-parametric statistical methods. A total of 7,524 snails (4081 in OR and 3443 in RFPs) belonging to ten species were collected. The species and their overall relative proportions are: Bulinus globosus (1.5%), B. truncatus (1.7%), B. forskalii (0.2%), Biomphalaria pfeifferi (11.0%) Potadoma moerchi (36.0%), P. freethi (6.9%), Melanoides tuberculata (40.0%), Lanistes libycus (0.9%), Lymnaea natalensis (0.7%) and Gyraulus costulatus (1.1%). The density of the snails varied seasonally and spatially according to a pattern common to most species. The seasonal pattern was basically unimodal with peak in either November/December or March/April for most species. Factors identified as affecting focal and seasonal distribution of snails were rainfall, pH, oxygen concentration, conductivity and presence or absence of macrophytes. Out of a total of 11 dominant macrophytes identified, only Ludwigia erecta served as indicator species for the presence of B. globosus, which is the established intermediate host of urinary schistosomiasis in Ile-Ife area. Fuirena umbellata and Commelina africana suspected to have some molluscicidal effect correlated negatively with B. truncatus (in RFPs) and Lanistes libycus (in OR), respectively. The likelihood of M. tuberculata as competitor snail against B. pfeifferi is discussed.