A population's dietary niche, including the extent of individual variation and specialization, plays a crucial role in shaping evolutionary trajectories, influencing both ecological interactions and morphological adaptations. Within-population variation in individuals’ dietary niche can drive differences in selective pressures, which can in turn impact adaptive divergence of trophic morphologies. As such, characterizing a population's dietary niche, including variation among individuals in relation to space and morphology, is a key focus for evolutionary ecologists. In this study, we examined diet variation and specialization in threespine stickleback (Gasterosteus aculeatus) in relation to trophic morphology across ecologically distinct sites in Lake Mývatn, Iceland. Stickleback in the population were dietary generalists, with within-individual variation exceeding between-individual variation across the lake and within most sites. However, individuals with more specialized diets came predominantly from a single location and were more likely to have a pelagic and/or epibenthic diet. We found that diet variation was associated with body size and trophic morphology. Body length was the strongest correlate of diet, with smaller individuals consuming more cladocerans and larger individuals eating more chironomid larvae, mollusks, and stickleback eggs. Gut length (relative to body size) was the next strongest correlate, with longer guts linked to hard-bodied prey and shorter guts to stickleback eggs. Gill raker length and the shape of the opercular region were also associated with diet variation, suggesting functional feeding differences. While the full range of dietary and morphological variation was present at most sites, we observed spatial variation in diet after controlling for trait variation, likely due to differences in food availability. Individual specialization was not predicted by trophic morphology. Our results highlight morphologically associated diet variation and spatial variation in diet and specialization in Mývatn stickleback, despite the population being primarily generalists with limited spatial genetic differentiation.