I don;t know if it's required, but the time I went, it was so full of tubes you could not have swam in it.
You can put the tube around your waist and let your body hang in the water rather than sit/lay on top of it. I did that some to cool off when it got too hot. That way, you won't be all in the sun but get to relax, too. Relaxing is the main point to me!