Nagle, EF, Nagai, T, Beethe, AZ, Lovalekar, MT, Zera, JN, Connaboy, C, Abt, JP, Beals, K, Nindl, BC, Robertson, RJ, and Lephart, SM. Reliability and validity of a pool-based maximal oxygen uptake test to examine high-intensity short-duration freestyle swimming performance. J Strength Cond Res 33(5): 1208-1215, 2019-A modality-specific swimming protocol to assess maximal oxygen uptake (V[Combining Dot Above]O2maxsw) is essential to accurately prescribe and monitor swimming conditioning programs. Consequently, there is a need for a reliable and valid graded intensity swimming pool test to accurately assess V[Combining Dot Above]O2maxsw using indirect calorimetry. The purpose of this study was to assess (a) reliability of an intensity self-regulated swimming pool test of V[Combining Dot Above]O2maxsw and (b) validity of a V[Combining Dot Above]O2maxsw test using performance swim (PS) time as the criterion. Twenty-nine men (n = 15) and women (n = 14) (age, 23 ± 6.4 years; body mass index, 23.5 ± 3.0 kg·m) performed 2 swimming pool V[Combining Dot Above]O2maxsw trials (V[Combining Dot Above]O2maxsw A and V[Combining Dot Above]O2maxsw B), and 2 PS tests (45.7 m [31.20 ± 4.5 seconds] and 182 m [159.2 ± 25.5 seconds]). For test-retest reliability (trials A vs. B), strong correlations (p < 0.05) were found for V[Combining Dot Above]O2maxsw (ml·kg·min) (r = 0.899), O2 pulse (ml O2·beat) (r = 0.833), and maximum expired ventilatory volume (L·min) (r = 0.785). For performance validity, moderately strong correlations (p < 0.05) were found between V[Combining Dot Above]O2maxsw A and 45.7-m (r = -0.543) and 182-m (r = -0.486) swim times. The self-regulated graded intensity swimming pool protocol examined presently is a reliable and valid test of V[Combining Dot Above]O2maxsw. Studies should consider the suitability of a V[Combining Dot Above]O2maxsw test for military personnel, clinical populations, and injured athletes.