Projecting individual-level performance of freshwater species is essential in understanding geographic limits of populations and forecasting how climate change is shifting these limits. Such projections can be made with bioenergetic models, which employ an energy balance equation to estimate daily energy gains via consumption and daily energy losses via respiration. This daily energy budget can then be summed throughout the year to project end-of-year body mass, seasonal changes in body condition, and ultimately survival. We provide an example of bioenergetic modeling on an imperiled and economically important native species—the Eastern Brook Trout (Salvelinus fontinalis). Our study area of 25,379 interconfluence stream segments is within the Tennessee River system and encompasses the species’ southern range limit, a critical area for their conservation. Our objective was to validate the bioenergetics model and then spatially and temporally project growth for three age-classes. To validate our models, we resampled 1,000 parameter sets, projected growth with these sets for 365 days, and compared end-of-year body mass with field-based mass-at-age data at four streams putatively occupied by brook trout. First, we projected spatial variation in growth and survival for a contemporary temperature regime. We found end-of-year mass increased with elevation and survival probabilities of ≥50% occurred at 1038, 1069, and 993 meters above sea level for age 0, 1, and 2, respectfully. Second, we projected changes in end-of-year mass and survival for the end of the 21st century time period using the RCP 4.5 climate scenario. We found decreased end-of-year mass and survival with elevational limits shifting upslope. In summary, we utilize individual-level growth and survival to estimate population-level range limitations for a cold-water species in Southern Appalachia. Bioenergetic modeling can identify suitable habitat for reintroduction, prioritize at-risk locations for management guidance, and infer shifting range limits with climate change scenarios for freshwater species.