I do not have asthma, but I have experienced trouble breathing in some indoor pools.  The explanation that I got from our coach was that the pool was recently shocked with chlorine and this was the effect of gases hovering above the water.  To answer your question, I don't think that your theory is that far-fetched and I believe it is very possible.  My suggestion to you is: 1. swim outdoors if possible, or 2. try swimming in another indoor pool if you can't go outside.

I am not a swimmer, per se, but a runner. I have asthma ONLY when I run. I have been told this is not an uncommon "event"...it's called "exercised induced asthma"..anyone can get it from any form of exercise. (I only know one other person with this). Only answer is to try many different recognized asthma meds. There are also some good herbs, etc., but I don't remember which one worked for me, as it was 6 or 7 years ago I tried it out of desperation from a friend. Whatever it was.....it WORKED great. Wish I could help you. Perhaps you should ask a GOOD health food store or herbalist. Good luck!

In fact swimming is one of the best forms of exercise for people with asthma because it usually causes the least amount of chest tightness.