I need to get in shape to swim

The health club I pay $$ to that I've been very lax about actually going to has both indoor & outdoor pools, so I really don't have much of an excuse.
One of the things I do like about swimming is it's more gentle on the body & is good cross-training. Plus when I tore my Achilles heel running & was out of commission for a while, the swimming helped w/ recovery.
Cheers.