Swimming helps in many beneficial ways! 30mins of swimming helps to reduce risk of coronary heart disease by 40%, lower bad LDL and increase your good cholestrol. It helps to lower risk of diabetes and gives you a good dose of endorphines hence reducing your stress level!
If you are hesitant to do exercises due to pain in your arthritic knees and low back, buoyancy support from the water helps to decrease loading onto your painful joints. Why not throw on some of your lovely bathers and start being a water baby!