Nagle, EF, Sanders, ME, Gibbs, BB, Franklin, BA, Nagle, JA, Prins, PJ, Johnson, CD, and Robertson, RJ. Reliability and accuracy of a standardized shallow water running test to determine cardiorespiratory fitness. J Strength Cond Res 31(6): 1669–1677, 2017—A standardized fitness assessment is critical for the development of an individualized exercise prescription. Although the benefits of aquatic exercise have been well established, there remains the need for a standardized nonswimming protocol to accurately assess cardiorespiratory fitness (CRF) in shallow water. The present investigation was designed to assess (a) the reliability of a standardized shallow water run (SWR) test of CRF and (b) the accuracy of a standardized SWR compared with a land-based treadmill (LTM) test. Twenty-three healthy women (20 ± 3 years), with body mass index (23.5 ± 3 kg·m−2), performed 2 shallow water peak oxygen consumption (V[Combining Dot Above]O2peak) running tests (SWRa and SWRb), and 1 V[Combining Dot Above]O2max LTM. Intraclass correlation coefficients indicated moderately strong reliability for V[Combining Dot Above]O2peak (ml·kg−1·min−1) (r = 0.73, p < 0.01), HRpeak (b·min−1) (r = 0.82; p < 0.01), and O2pulse (V[Combining Dot Above]O2 [ml·kg−1·min−1]·HR [b·min−1]) (r = 0.77, p < 0.01). Using paired t-tests and Pearson's correlations, SWR V[Combining Dot Above]O2peak and HRpeak were significantly lower than during LTM (p ≤ 0.05) and showed moderate correlations of 0.60 and 0.58 (p < 0.001) to LTM. O2pulse was similar (p > 0.05) for the SWR and LTM tests with a moderate correlation of 0.63. A standardized SWR test as a measure of CRF is a reliable, and to some degree, valid alternative to conventional protocols and may be used by strength and conditioning professionals to measure program outcomes and monitor training progress. Furthermore, this protocol provides a water-based option for CRF assessment among healthy women and offers insight toward the development of an effective protocol that can accommodate individuals with limited mobility, or those seeking less musculoskeletal impact from traditional land-based types of training.