Rising temperatures are set to imperil freshwater fishes as climate change ensues unless compensatory strategies are employed. However, the presence of additional stressors, such as elevated nitrate concentrations, may affect the efficacy of compensatory responses. Here, juvenile silver perch (Bidyanus bidyanus) were exposed to current-day summer temperatures (28oC) or a future climate-warming scenario (32oC) and simultaneously exposed to one of three ecologically relevant nitrate concentrations (0, 50 or 100 mg L−1). We measured indicators of fish performance (growth, swimming), aerobic scope (AS) and upper thermal tolerance (CTMAX) to test the hypothesis that nitrate exposure would increase susceptibility to elevated temperatures and limit thermal compensatory responses. After 8 weeks of acclimation, the thermal sensitivity and plasticity of AS and swimming performance were tested at three test temperatures (28, 32, 36oC). The AS of 28oC-acclimated fish declined with increasing temperature, and the effect was more pronounced in nitrate exposed individuals. In these fish, declines in AS corresponded with poorer swimming performance and a 0.8oC decrease in CTMAX compared to unexposed fish. In contrast, acclimation to 32oC masked the effects of nitrate; fish acclimated to 32oC displayed a thermally insensitive phenotype whereby locomotor performance remained unchanged, AS was maintained and CTMAX was increased by ∼1oC irrespective of nitrate treatment compared to fish acclimated to 28oC. Growth was however markedly reduced in 32oC-acclimated compared to 28oC-acclimated fish. Our results indicate that nitrate exposure increases the susceptibility of fish to acute high temperatures, but thermal compensation can override some of these potential detrimental effects.