You will need:
1) iPod shuffle or any small mp3 player
2) WATERPROOF headphones. I paid $11 on Amazon
3) Small party balloon (a dozen costs $1 at most stores)
5) goggles and swimming cap
DISCLAIMER: Try at your own risk. Mine works great, but I cannot be responsible for your ipod. Use a NEW balloon before each workout.
Step 1: Insert iPod in balloon
Step 2: Insert headphone cord inside balloon
Step 3: Seal balloon opening
Step 4: Check before using, then go swim!
This is what it looks like installed under my swim cap. I have to turn it on before I swim, but I can control the song shuffling during swim. Putting one or both of my goggle straps under the iPod helps secure it fine.