Hopefully you have been "swimming" in the bathtub.
If you haven't taken your child swimming all winter - do it soon! Your child may have already forgotten much of what he learned. You need to treat the time at the pool as a new adventure! Don't have expectations. Your child will look at the water with more mature eyes. His attitude of joy and excitement will depend on you! Show him how you like the water. Go under the water first and swim to him. Laugh and enjoy it.
Turn on my Learn to Swim with Miss Bea dvd, and watch it again and again and your child will see himself in one of the kids that are having fun and learning how to swim.