We explored whether increased river flows negatively affected growth of largemouth bass (Micropterus salmoides) in the lower Ouachita River, Arkansas. To test this hypothesis, largemouth bass (n = 460) were collected during 2008-2010 from the Felsenthal Reservoir region of the river. Largemouth bass were aged and annual growth increments were calculated using standard back-calculation techniques. Growth of largemouth bass was relatively rapid in the Ouachita River, with von Bertalanffy growth model parameters determined as L∞ = 513 mm, K = 0.324, and tο = -0.314; catch-curve analysis estimated that total annual mortality of the population averaged 48% (95% CL 42%-54%). Back-calculated growth increments of largemouth bass were compared across years classified as "high-flow," "low-flow," and "average-flow" based on analysis of historical June-October hydrology (i.e., corresponding with the largemouth bass growing season). Two-way factorial ANOVA analyses indicated that largemouth bass growth was lower during high-flow years, with the effect most pronounced for the age 2-4 cohorts. Results suggested that high-flow periods typically beneficial to fishes in large river-floodplain systems may not always result in increased growth rates in more highly regulated river systems such as the Ouachita River. Better understanding of fish growth-hydrology relationships will become increasingly important in light of predicted future effects of climate change, which include increased frequencies of hydrologic extremes.