When is it okay to put baby in a pool?

I've seen pictures of teeny tiny babies in pools and they look so happy and relaxed but it makes me nervous lol. We were thinking of taking a small trip for Christmas but baby will only be a little over a month old and I know once he's here I'll be able to gage things differently from how he does with bath time and how well he supports himself and things but for now I'm curious. Of course he'd be in a float and i'd be right beside him the whole time.