OBJECTIVE The purpose of this study was to physiologically compare submaximal intensity deep water running (DWR) and treadmill running (TMR) exercise in trained athletes. METHODS Pre-test, post-test, 2 x 2 factoral design. METHODS Treadmill exercise tests occurred in the Human Performance Laboratory. DWR trials took place in the deep end of the University pool. METHODS Seasonally trained college-aged male cross country runners (N = 8). Subjects completed a treadmill maximal oxygen consumption (VO2max) test, followed by a submaximal treadmill and deep water run at heart rates equivalent to 60% and 80% treadmill VO2max. METHODS Oxygen consumption (VO2), ventilation (VEstpd), rates of perceived exertion (RPE), energy expenditure (kcal.min-1), respiratory exchange ratio (RER), fat and carbohydrate oxidation (g.min-1) were measured during two 5 minute steady state stages for both trials. RESULTS The trial by intensity interaction for VEstpd was significant, demonstrating greater ventilation during DWR as compared to TMR at 80% VO2max. The main effect of trial demonstrated that significantly higher RER and carbohydrate oxidation, and lower fat oxidation occurred during DWR as compared to TMR. VO2, RPE, and energy expenditure did not differ significantly between trials. CONCLUSIONS DWR is a comparable form of submaximal intensity exercise as TMR in well-trained athletes. DWR does, however, maintain unique properties that differs it from TMR. Therefore, the concept of training specificity should be further considered when prescribing DWR and using it as an enhancement tool or substitute for dry land running.