Timber harvesting in Alberta's boreal forest has recently increased. It is imperative to collect pre-harvest data on lakes of the region to evaluate potential logging effects. Stable isotope analysis and fish stomach content analysis were used to characterize food webs and determine the importance of external and internal carbon sources in lakes with different fish assemblages prior to harvesting. Consumers in lakes with water residence times $>$1 yr primarily used internal carbon inputs, whereas in lakes with water residence times $\leq$1 yr, consumers primarily used external inputs. Fathead minnows and northern pike were omnivorous and often occupied similar trophic levels. Pike feeding habits were flexible as their prey base changed. A prevalence of omnivory in fish and invertebrates, and the apparent generalist feeding habits of certain fish species, suggests that organisms may be flexible in their feeding habits in the face of altered food webs due to logging.