Environment plays a central role in shaping population dynamics and life history. Abiotic variables can provide insight into resource availability and habitat selection. In this thesis, I identified environmental drivers behind the abundance and size-at-age of the main commercial species, Lake Whitefish, Coregonus clupeaformis, in Great Slave Lake (GSL), Northwest Territories using Gaussian spatial random fields (SRFs) applied within a Bayesian framework. In Chapter 2, I developed standardized indices for numbers and mean weight of Lake Whitefish in the commercially fished western basin, resulting in more precise measures for catch-per-unit-effort to identify temporal trends in abundance. I estimated model parameters for both responses using soak time, smoothed year, and the random effects of SRFs by design, and considered the effects of water temperature, turbidity, distance to the nearest shore, and distance to the southern shore. The model for numbers did not include any environmental variables, but the model for mean weight was influenced by water temperature, distance to the nearest shore, and distance to the southern shore. Ontogenetic shifts in habitat were seen with higher densities of smaller, younger fish near the mouth of the Hay River, extending centrally into the basin, and with larger, older fish diffusing out to northern regions of the western basin. In Chapter 3, I explored the impacts of the environment on Lake Whitefish fork length-at-age. Using models for immature and mature fish, I examined the effects of sex, smoothed age, and the random effects of SRFs and capture year by design and considered the effects of water temperature, turbidity, and site depth. Water temperature was important regardless of reproductive stage, while sex had no effect. The SRFs depicted similar spatial distributions of size-at-age, with hotspots of greater size-at-age attributed to local movement away from higher densities of smaller size-at-age associated with riverine inputs along the southern shore. Chapters 1 and 4 provide background and context to interpret the results. The results of this thesis highlight the importance of river-lake interactions in GSL, which have been identified as driving the life history and population dynamics of the commercially and ecologically valuable Lake Whitefish.