Swimming's really good for losing weight, no sweating and less knee pain involved. Wish I had a private pool too, you can definitely tell the public ones are 30% filled with piss.
Your metabolic rate can be several times higher in a pool or other body of water than it is on land without any exercise at all. Body heat is lost at a much higher rate when you are submerged in water and your body will burn more fuel to maintain core temperature.
Swimming is amazing for the elderly as well as the heavily obese. Buoyancy takes all the load off joints/cartilage and significantly reduces wear or arthritic pain while still providing consistent, firm resistance to movement that burns calories.