As predators are generally larger than their prey, positive body size and trophic position relationships are typically assumed, and these relationships have helped in estimating and predicting the effects of global environmental change on the trophic dynamics of aquatic ecosystems. However, current efforts to confirm the generality of body size-trophic position relationships have focused mainly on interspecific patterns using species-aggregated and averaged data, and little effort has been devoted to assessing how trophic position scales with body size at the intraspecific and community levels as well as exploring its ecological drivers, particularly for fishes in freshwater ecosystems. To fill this gap, we present a broad-scale study of body size-trophic position relationships in freshwater ecosystems at both the intraspecific and community levels using an individual-based body size and isotopic signature dataset that includes 2564 samples of 65 fish species in China. Our results indicate that body size-trophic position patterns at both the intraspecific and community levels can be positive, negative or insignificant. Non-significant patterns predominated at both levels, with slightly more than 30 % showing positive relationships, which highlights that the positive body size-trophic position pattern is not universally prevalent and that body size should be used with caution as a proxy for the trophic position of fishes at both the intraspecific and community levels in freshwater ecosystems. No factor was related to body size-trophic position patterns at the community level, while habitat type, elevation, temperature and fishing pressure were identified as the key determinants of body size-trophic position patterns at the intraspecific level, implying that fishing and climate warming can shift the food-web size structure of freshwater ecosystems by affecting population trophic dynamics.