Objective: To investigate the effectiveness of an 8-week aquatic program on cancer-related fatigue, as well as physical and psychological outcomes in breast cancer survivors. Design: A randomized controlled trial. Setting: Outpatient clinic, urban, academic medical center, and a sport university swimming pool. Participants: Breast cancer survivors (N=68) were randomly assigned to either an experimental (aquatic exercise group in deep water pool) group or a control (usual care) group. Interventions: The intervention group attended aquatic exercise sessions 3 times per week for 8 weeks in a heated deep swimming pool. Sessions lasted 60 minutes in duration: 10 minutes of warm-up, 40 minutes of aerobic and endurance exercises, and 10 minutes of cool-down exercises. Patients allocated to the usual care group followed the oncologist’s recommendations in relation to a healthy lifestyle. Main Outcome Measures: Values for fatigue (Piper Fatigue Scale), mood state (Profile of Mood States), and abdominal (trunk curl static endurance test) and leg (multiple sit-to-stand test) strength were collected at baseline, after the last treatment session, and at a 6-month follow-up. Results: Immediately after discharge, the aquatic exercise group showed a large effect size in total fatigue score (d=.87; 95% confidence interval,.48-1.26), trunk curl endurance (d=.92; 95% confidence interval, 1.97-3.83), and leg strength (d=1.10; .55-2.76), but negligible effects in vigor, confusion, and disturbance of mood (d<.25). At the 6-month follow-up period, the aquatic exercise group maintained large to small effect sizes in fatigue scores, multiple sit-to-stand test, and trunk curl static endurance (.25>d>.90) and negligible effects for the fatigue-severity dimension and different scales of the Profile of Mood States (d<.25). Conclusion: An aquatic exercise program conducted in deep water was effective for improving cancer-related fatigue and strength in breast cancer survivors. Archives of Physical Medicine and Rehabilitation 2013;94:221-30 (C) 2013 by the American Congress of Rehabilitation Medicine