Let me qualify what I said about weight loss. Of course you can lose weight from swimming. What I meant was if you pick up swimming as a novice and as something to do besides cycling over the winter, you likely won't lose weight. For one thing the cold water creates hunger for most people because your body wants to make up for the cold. That creates a craving for more food. Your body also adapts to cold water by retaining fat for both warmth and buoyancy. This is just at first during the initial few weeks. But if you do it as a winter activity, you may not lose weight unless you concentrate on food intake.

Also swimming a mile burns around 400 calories. It takes time to swim unless you are next door to a pool. For most people that means gathering up your gear, driving somewhere, change, swim, shower, get dressed, and drive home. So it's a two hour effort to burn 400 calories. Then you are starving and stop at McDonalds for a Quarter Pounder, fries, and of course a diet coke.