Fishes have specific dissolved oxygen and water temperature requirements needed to promote optimal growth. Ongoing anthropogenic climate change will lead to increased water temperature and likely changes in dissolved oxygen concentrations that will affect fish populations in a variety of ways. This study uses high-frequency, automated sensor data from 2011–2015 to examine dissolved oxygen and water temperature in Lake Lillinonah, a hydroelectric impoundment in western Connecticut, to identify potentially stressful conditions for Esox lucius (Northern Pike [NP]) and Micropterus salmoides (Largemouth Bass [LMB]). We found that summer water temperature was nearly always in an optimal range for LMB growth, but was frequently in the stressful range for NP growth. In addition, in some years, Lake Lillinonah experienced consistent hypoxia, reducing the thermal refuge available for NP. Long-term data from Lake Lillinonah show an increase in mean July surface water temperature, and further temperature increases are expected as the climate continues to warm. This trend, coupled with a potential reduction in thermal refuge due to hypoxia, poses serious consequences for NP, given that current conditions frequently exceed documented optimal growth range for the species.