Regular swimming builds endurance, muscle strength and cardio-vascular fitness. It can serve as a cross-training element to your regular workouts. Before a land workout, you can use the pool for a warm-up session. Swimming with increasing effort to gradually increase your heart rate and stimulate your muscle activity is easily accomplished in the water. After a land workout, swimming a few laps can help you cool-down, move blood through your muscles to help them recover, and help you relax as you glide through the water.

Many swimmers find an in-direct benefit form swimming. They develop life skills such as sportsmanship, time-management, self-discipline, goal-setting, and an increased sense of self-worth through their participation in the sport. Swimmers seem to do better in school, in general terms, than non-swimmers as a group.
Dr. Mathew Luebbers - Sports Science from United States Sports Academy

Swimming is a great form of exercise and the benefits to our health are numerous. Exercise is key to weight management, a healthy heart and greater energy levels, and, coupled with a sensible diet, is essential for us all to live a long and healthy life.
British Heart Foundation

Swimming enhances balance, strength, coordination, endurance, and promotes health & fitness. Sport, and swimming in particular, provides an opportunity for children to succeed when they may not do as well in the classroom for example. Swimming also has many benefits for children with disabilities.
Swim School Owners Association of Australia

For every child who drowns, three receive emergency department care for non-fatal submersion injuries. More than 40% of these children require hospitalization (CDC 2003). Nonfatal incidents can cause brain damage that result in long-term disabilities ranging from memory problems and learning disabilities to the permanent loss of basic functioning (i.e. permanent vegetative state).
Dr. Gregory Fort California University