Yes, my 14 year old daughter has swum for about 8 years. She is sidelined now from patella tendonitis and I can't wait till she gets back in the water!!!!
Here's her protocol, after much deliberation and years of experience. My daughter swims about 3,000 yards for a workout (I think) or for about 1 1/2 hours. They also do drylands, so that may add 1/2 to 1 hour to the practice.
For a 5:30 practice, the basal rates go to -0- at 3:00 (2 1/2 hours before swimming). She still wears the pump, becasue she wants to snack and eat and all before getting in the water and she has to have the pump to bolus. She does her regular practice, and she checks proactively every 45 minutes. She makes it through the practice now without getting low. She should (but doesn't becasue she's 14) check and make up some insulin when getting out of the pool since there's no IOB for so long. I think that piece is critical to not go high later in the evening.
Now we met a gal from Australia at Children's Congress in 2007 who did the exact opposite. She said she got HIGH during practice...go figure. It makes much more sense to cut back on insulin for a practice than give more insulin. For meets, she did get high, probably due to the adrenalin.
Hope that helps. I should get my daughter to join juvenation to chat with you. How old are you? AS I said, my daughter is 14. She was swimming Seniors when she got injured. Watch the breaststroke!