Which muscles does swimming work?

I'm joining a swimming class for the summer, and am going to be doing hour long work-outs five days a week. I build muscles rather fast, but I haven't worked out in a long time and have almost none right now. I specifically want to know how much it works out your ab muscles. And does it give you more... show more I'm joining a swimming class for the summer, and am going to be doing hour long work-outs five days a week.
I build muscles rather fast, but I haven't worked out in a long time and have almost none right now.

I specifically want to know how much it works out your ab muscles. And does it give you more muscles, or does it more work on flattening your stomach?

Also, how long (approx. i know it varies person to person) do you think it will be before I really start seeing a difference?
I'm 5'4" 5'5", somewhere in that area, and weigh between 125 and 130.
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