We assessed the dynamics of the littoral fish assemblage in Spirit Lake, Iowa, and examined potential consequences of these dynamics for availability of prey fish for piscivores. Using beach seines, we quantified the annual, seasonal, and spatial variation in density and biomass of the entire assemblage and of component species over a 4-year period. Potential prey fish availability was inferred from the biomass of the cumulative total fish length groups and sizes of fish eaten by piscivores. Total fish density and biomass averaged 10,024 fish/ha and 276.3 kg/ha, respectively. Density and biomass of total fish varied among years and seasons, but seasonal patterns differed among years. Yellow perch Perca flavescens, bluegill Lepomis macrochirus, walleye Stizostedion vitreum, and common carp Cyprinus carpio were the predominant species overall, but the proportional species composition of both total density and total biomass varied highly. Changes in the fish assemblage resulted in dramatic changes in the potential availability of prey fish over time and with piscivore size. These dynamics could lead to variable growth and condition of resident piscivores as well as to variable success of stocking fingerling piscivores.