Summer time, swimming time (muscle cramps:S:S)

The weather is getting warmer and warmer each day. This could only mean one thing; the time has come to jump in the pool. We have a swimming pool at our farm, and for the past two weeks we have been going for a swim on Fridays. I love to swim. I especially love to swim when the sun is still shinning. My cousins tend to avoid swimming during duhr time just out of fear they would get dark. They say 'we have weddings coming up, we should swim around 5pm or so' . The things is, i dont really care. Even if i was the bride i wouldnt care. For me, the most important thing is that i have a good time. So this past friday, it was only me and my little cousins in the pool. The rest were under a shade watching from distance. So i had a good time. I have one issue, i get muscle cramps while swimming all the time. It happend to me in Canada, and it is happening to me here! In Canada, i wasnt so scared of it because there was always a life gurad and whenever it occurs i have been rescued out and given oxygen and all that is necessary. Here though, we dont have a life gurad, it is not a public pool so yeah. This Friday i didnt get any muscle cramps because what i did was swim for one round, rest for few mintues, then do another round. Then rest. Then walk around the water, then swim for another round.I'm not a perfect swimer, but i'm ok. I dont know all the ways. Unlike my mom, she is a perfect swimer. She just lots abit of her speed due to her lack of practice. Anyways, after 20 mintues or so of being at the pool i got out of the pool because i thought i better get out before my muscles cramp. They did the Friday before this (after 20 mintues of swim time to be exact). It was me and my two cousins swimming, i was teaching my cousin this easy way of swimming but after reapting the way for few times my muscles cramped. The good news was, that both of my cousins were around me, and we werent in the deep end. So one held my foot and stablized it so it wont move, and the other pulled me from my hand until i got to build in seats at the babies end. I sat crying the pain out. But at least i was safe. So did any of you ever experiences muscle cramps? for me, it happens all the time, and it is painfullllllllllllllll. It is very painful. I would drawn so easily even at the shallow water. My height is 1.70 i could stand rasing my toes a little at the end of the pool and be able to breath easily (that works if i got tired from swimming) but if my muscle cramps occurs i would drawn period. What should i do? anyone knows?