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Human activities have transformed the landscape and altered geochemical pathways through intensive land uses such as agriculture and urbanization. This study quantified the individual and cumulative influence of land-use drivers on nutrient concentrations for 29 Ontario tributaries flowing to Lake Erie and Lake Huron. For each watershed, measures of agriculture, urbanization and population served by municipal sewage treatment plants were quantified at multiple spatial scales; stream-water nutrients (nitrogen, N, and phosphorus, P) were sampled on 10 occasions between May and November 2012, and were also compiled from government records for concurrent (2012) and prior (2007, 2008, 2011) years. Application of ordinary least squares regression analysis showed that in 2012, concentrations of N and P (total as well as dissolved forms) were primarily driven by sewage treatment and urban activity, with agricultural activity as a secondary influence on variability. Evaluation of model predictive performance under scenarios of varying climate (wet, dry and ‘normal’ conditions) and spatial coverage (i.e. broader than the original sampling sites) showed that stream nitrogen concentrations could be predicted, on average, 36–85% of the time; phosphorus forms were, however, not successfully predicted, likely due to differences in sampling frequency relative to runoff events. The finding that both urban and agricultural land-use activities influence nutrient concentrations in Canadian tributaries to lakes Erie and Huron underscores the need to reduce both point and non-point inputs in order to mitigate eutrophication of downstream lakes.