Hi! Being a competitive swimmer, I have tried it all - I find that using a clear top coat over the nail colour is the best fix. Also, make sure your nails remain moisturized - the pool as well as nail colour tends to dry nails out. I find that nail colour will last longer when nails are in better condition. I would try O.P.I.'s clear top coat and Sephora's cuticle oil pen. I hope that was helpful!
ph07 has provided you with excellent advice! A base coat and a top coat will always help in making sure your nail colors last longer. OPI's 3 Nail Treatment - 3 in 1 Base, Top, & Strengthener is a fantastic option. I often find that after swimming, taking a long bath, or washing my dogs that my cuticles are super dry. My favorite fix for this is Josie Maran's Aragon Oil, it leaves the bases of my nails refreshed.
A really cheap way to fix the fading and chipping is to get drugstore nailpolish with the thin brushes, and after painting them once wait a long time for the nail polish to dry. Apply a clear coat. The next day, apply another clear coat! If you apply several clear coats, the nail polish is practically indestructable (even when touched by nail polish remover!!)
For me, there are 2 brands i like for swimming.
The cheap version- Sally Hansen "Hard as nails" polishes.
The more expensive version- OPI nail polishes.
They both come in lots of cute colors that look really pretty underwater!