I recommend swimming post workout,for a couple of reasons you probably already know. Same day, next day, whatever.
One of the reasons for the discomfort after lifting is microtorn muscle fiber, and your whole bodys musculature is what keeps you standing. So naturally sore muscles = you want to lie down and take load off those muscles. Shoulders, neck, back, legs especially.
But in a pool, that pull of gravity is lifted and it becomes much easier to move around, stretch etc which is important for promoting healing. Whether it's warm or cool, water submersion is just a soft of natural cast that takes pressure off of your sore parts, not to mention it's a relaxing way of chilling out.
And you can still take the nap after. For me, working out, a nice swim, and a nap are a trifecta. There is probably science research out there that supports all this, but personal anecdote, it works.