In freshwater systems, the threat from a myriad of environmental stressors is prominent, including stress from nutrient effluents (i.e. nitrates) and altered pH regimes. Environmental stressors can disrupt organismal energy homeostasis and physiological performance via reductions in aerobic scope (i.e. maximal – routine oxygen uptake). Independently, nitrate and low pH affect energy allocation by increasing maintenance costs and disrupting oxygen uptake. The interaction between these two stressors may result in synergistic reductions in aerobic scope and subsequently reduce whole animal performance (e.g. swimming performance and growth rates). We explored the interactive effects of elevated nitrate and low pH on the energetic costs on the freshwater fish, spangled perch Leiopotherapon unicolor. Fish were exposed to a factorial combination of two pH levels (pH 4.0 and 7.0) and three nitrate concentrations (0, 50 and 100 mg/L). It was predicted that combined exposure to low pH and elevated nitrate concentrations would result in synergistic decreases in aerobic scope and performance. We show how aerobic scope, blood –oxygen carrying capacity and whole animal performance are affected by the interaction between nitrate and low pH and provide an insight into the possible mechanisms allowing fish to persist in degraded environments.