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Extremes of flow and patterns of flow variability limit the distribution and abundance of riverine species via a natural disturbance regime. Using a habitat template approach, we describe the distribution and characteristics of natural flow regimes in Canada based on the severity of flows, flow predictability, and flow variability. Bayesian clustering was used to group 888 gauged watersheds across Canada into 10 classes. Some flow classes were found in all provinces, whereas others showed greater regional grouping related to land physiography (e.g., Canadian Shield and ecozones). Ontario and British Columbia had the greatest diversity of flow classes. Larger river systems tended towards less harsh flow regimes and greater flow regularity than small systems. A stream-lake network pattern, particularly the presence of lakes, decreased the severity of flow. The flow metric flood-free interval was found to be a potentially misleading indicator of reduced disturbance for high-latitude streams in Canada where ice formation and persistence are important stress factors for biota. Most flow stations had an 80% or higher chance of belonging to their primary membership class. Quantifying uncertainty in class assignment can help fellow scientists and resource managers appropriately apply our findings. [ABSTRACT FROM AUTHOR]