Book excerpt: Summarizes the major modelling projects undertaken to model water quality in the Peace, Athabasca, and Slave river systems. The first section describes the scope of the problem of modelling water quality in large complex systems that are relatively oligotrophic, located at relatively high altitudes, and experience highly seasonal environmental fluctuations. It also provides a summary of the models used to predict key water quality variables. Section 2 gives a general overview of the utility and shortcomings of water quality models, with the goal of establishing key criteria for assessing the successes of models developed by the Northern River Basins Study (NRBS). Section 3 summarizes key findings of the NRBS models and evaluates the results against criteria outlined in section 2. Section 4 presents a series of recommendations for modelling dissolved oxygen, transport and fate of contaminants, and distribution of contaminants in the food chain, along with strategic suggestions for future work.