Background and Purpose: Quantifying how the environment (land vs water) influences age-related changes in postural sway is important for the development of new therapies that improve balance. The authors are not aware of any previous studies that have compared postural sway in an aquatic environment between age groups or when water depth and/or perturbations are incorporated into the comparison. The purpose of this study was to compare the effect of water depth and jet intensity on postural sway in older and younger adults. Methods: Sixteen older (age = 62.8 ± 9.56 years) and 15 younger (age = 22.5 ± 1.85 years) adults participated. Participants stood quietly for 90 seconds on land and at various water depths and jet intensities while center of pressure (CoP) sway was recorded using a force platform. Results: Statistical comparisons revealed that CoP range and area measurements were different between land and aquatic conditions (P = .04 − .001). For example, CoP sway area in chest deep water (8.51 ± 2.97 cm2) was greater than on land (2.41 ± 1.37 cm2; effect size = 2.05). Furthermore, CoP sway area at the 60% jet intensity (71.4 ± 31.2 cm2) was substantially greater than at the 20% jet intensity (12.4 ± 6.23 cm2; effect size = 1.89). Surprisingly, the proportion of change across water depths and jet intensities was not consistent between older and younger groups as indicated by significant age by environment interactions (P = .03 − .001). Follow-up tests indicated that older adults swayed less than younger adults in water at the level of the hip (effect sizes = 0.42-0.94) and when water jets were applied at a 60% jet intensity (effect sizes = 0.63-1.97). Conclusions: Water immersion to the chest with high jet intensities produces the greatest CoP sway in both groups. This is likely a result of buoyancy and perturbation intensity. Less sway in the older group may reflect a strategy that reduces degrees of freedom for this group when faced with these stability challenges.