Swimming is the fourth most popular sports activity in the United States and a good way to get regular aerobic physical activity. Just two and a half hours per week of aerobic physical activity, such as swimming, can decrease the risk of chronic illnesses like heart disease and diabetes. For people with arthritis, swimming and other water-based exercises can improve the use of affected joints and decrease pain from osteoarthritis.
Source: www.cdc.gov/healthywater/swimming/swimmers/health_benefits_water_exercise.html