Meowbark, it is never a good idea to go swimming without protection! The only thing that "stops" the menstrual flow is pressure. There is more pressure of whatever pushing up into your uterus than there is of the blood coming out. If you were to cough, laugh or strain hard as you might do in swimming then you might eject stuff that you don't want to. Noone may notice but someone might. That and as soon as you get out of the pool the water is gone so your flow will immediately restart.... Not a good look to be heading off to the showers with bloodied pool water dripping down your legs and a waste of a good swim suit!
If your flow is light and it is the last couple of days then you might get away with it but I can also tell you that a lot of people don't believe it is in anyway acceptable to jump into a pool without menstrual protection. We don't urinate in the pool and you don't defecate in the pool.. menstruation is viewed on the same lines. Realistically, if you want to do that then you need to start looking at tampons. Not only are they good for swimming but it means you can wear tight clothes without a hassle and do a lot of other physical activities without worrying about the pad between your legs moving about and scrunching and leaking etc.