Hydrological models have large amounts of uncertainty in streamflow predictions. Using extra data (e.g. isotope tracers) helps evaluate whether the model is getting the right answers for the right reasons. In a Canadian basin, three types of isotope in precipitation input are used to drive a tracer-aided model and assess the resulting model uncertainty. This study shows how a tracer-aided model can be used at the larger scale, and that the model can be of value in such regions.