Densities of dominant macroinvertebrates declined in profundal and pelagic regions but not in littoral regions of Lake Lenore, Washington, after introduction of cutthroat trout Oncorhynchus clarki, Chaoborus flavicans, Hyalella azteca, and Callibaetis sp. composed over 90% of cutthroat trout diets, and these prey taxa showed the greatest response to the introduction. Although cutthroat trout selectively consumed larger individuals of these taxa and reduced mean length of prey in autumn populations, no change in size distribution of overwintering individuals was apparent 6 years after the fish were introduced. Reported changes in spatial distribution of these prey support the hypothesis that prey refuge space in littoral regions buffers prey populations from the direct effects of cutthroat trout predators.