The reason for such an observation is that the swimming pool water contains chlorine in high percentage. When this chlorine comes in contact of the acne, it irritates the skin leading to situation like inflaming the acne. This in turn aggravates the acne condition to a major extent.
One effective cure for acne is to make use of appropriate skin care supplements. One good option for you is exposed facial cleaner .

So if you are nursing acne, make sure that you avoid the plunge in the pool for some time.