As coupled climate change and human land use transform the hydrologic regimes of watersheds in Northwestern North America, endemic fishes may sometimes encounter novel temperature and flow conditions. Thermal performance curves offer a mechanistic description of the temperature-performance response function and might be able to predict individual-level responses to temperature conditions outside of historical norms. However, the degree to which novel temperature responses affect populations and communities is complicated by ecological contexts including physical habitat characteristics, phenology, and spatial population structure, among others. Here, we describe a coupled study which fit thermal performance curves through an exhaustive meta-analysis to predict thermal habitat suitability and coupled snorkel surveys to investigate whether thermal habitat suitability predictions translate to occupancy or density outcomes in a thermally diverse watershed. Collectively, we find that thermal performance might influence occupancy and density trends only once critical habitat characteristics and spatial structure have been accounted for. We conclude by detailing how our findings relate to persistence and resilience of populations facing thermal challenges associated with climate change.