3.  Cardiovascular system  Muscular system  Skeletal system  Digest system  Nervous system  Excretory system  Respiratory system  Immune system

4. Just two and a half hours of aerobic exercise, like swimming, reduces your risk for heart disease. Studies show that swimming may help you live longer, too.

5. Swimming is a for muscle-building exercise because the water provides resistance that makes the muscles work harder. This can result in an increase in both muscle strength and growth in size

6.  For those who already suffer from arthritis, water-based exercises and swimming help improve the use of the affected joints without additional pain or discomfort.

7.  In both cases, it is imperative to avoid eating right before entering the water, to allow your digestive system time to assimilate your food.

8.  To keep moving in the water, though, and push past water's resistance, your muscles need a steady and dependable source of nutrients to burn, as well as oxygen to fuel your metabolisum

9.  exercise helps your immune system to fight off bacterial and viral infections.

10.  The human excretory system relies on the functioning of the lungs, kidneys and skin to remove toxins from the body. The movement of blood through the body transports toxins from various parts of the organism to these excretory organs.

11.  Chlorine fumes are toxic and can affect the central nervous system.

12.  Live strong.com  Google.com