Bioenergetics modeling was used to quantify the consumption dynamics of lake troutSalvelinus namaycushin Flaming Gorge Reservoir, Utah–Wyoming. Analysis of diet and population estimates of different size-classes of lake trout indicated that kokaneesOncorhynchus nerkamade up the greatest proportion of prey biomass. Examination of growth rates of forage fish and predator–prey size ratios indicated that Utah chubGila atrariawere more vulnerable than kokanees to lake trout predation. Utah chub grow slower than kokanees and thus were susceptible to piscivores over a longer age span. We conclude that kokanees will make up an even larger proportion of the pelagic fish assemblage of Flaming Gorge Reservoir in future years.