What if my period starts while I'm swimming?!?

I'm going on holiday with my friend and her family for 6 days, and i have a feeling that im going to be on my period. i started about a year ago, and its still really irregular but i have been getting cramps for the last 2 weeks? we are going to butlins and the main thing to do for free is swim, but i have a really bad feeling i am going to start in the pool!? what do i do and would i know i did? because i really hope i dont have to sit out, and i can use tampons, but im kinda scared to use them to go swimming in case they leak, and i cant just put one in when im not on so, any advice?