Swimming is a non contact sport, so there is very little chance of injury or accidents happening. Your body is also supported by the weight of the water so it is an excellent form of exercise for those with back pain. Swimming is also an excellent form of aerobic exercise helping your circulation and stamina. Unlike some sports and physical activities it involves many muscle groups in the body which makes it good for all round health and vitality.
If you swim breaststroke, do keep your head low in the water especially if you have history of neck problems. Keeping your head right our of the water means you have to extend your neck heavily and can bring on a neck pain if done often for long periods.