How do i prevent calf muscle cramps during swimming?

You need to pay more attention to your hamstrings, calves, and tibialis anterior muscles. On your off days jump rope, do high repetitions of calf raises with low or no weight and do high but steady repetitions with low weight on the leg curl. For the tibialis anterior, face a wall, place your hands out in front of you against the wall and rock back so you end up balancing your weight on your heels. Roch from your heels to the normal foot position several times until you are moderately tired. From that same position, sway from side to side on the edges of your feet, lifting the sides of the feet but always maintaining contact with an edge of the foot on the floor. You need to use low weights, if any at all, and start builidng up high repetitions of these exercises in a moderate fashion. You're putting a lot of stress on the calf muscles relatively suddenly and forcefully in the dolphin kick and this probably the time they most contract. You have to get them used to being used out of the water and get them used to being used a lot so they don't react to your training load by cramping.

eat lots of potassium

DRINK ALOT OF WATER. and while your on your slow lap or a brake move our foot up and down too loosen the muscle.

Eat Banana's before you swim, and make sure to drink a lot of water beforehand, becuse as much as it doesn't seem like it, you are losing a lot of water while swimming, Banana's are great though for it, that's what i ate =)

I hate charlie horses too! they are just so annoying. i also get severe leg cramps that also happen in my thighs and toes. Bananas are good, but too much of them won't do anything. The potassium in them is whats good for you. Others food contain potassium too. Another thing you should do during practice is to drink gatorade. It replenished better than water and propel sports drink is okay too. Before you swim, try not to do too much running or legwork, it may tighten your muscles and cause a cramp later.