I think you've answered your own question, really.
I usually prefer to use public baths because of this problem. I'm type 1 and therefore it is possible that I could suffer a hypo and be unaware, which would put me at risk in a swimming pool. I wear diabetes ID silicon wristbands when I swim. Swimming is my main form of exercise. Interestingly, it doesn't always lower my blood sugar, sometimes it raises it considerably and then drops like a stone later in the day. Swimming slower might help this problem.
In the past, I used a gite swimming pool, when on holiday, but even there, I preferred to swim when my husband was nearby.
( I was actually more concerned there that the pool might not be safe from a quality of water point of view, and, in fact, I was really ill with a stomach-upset the week after the holiday. Though I can't prove any link between the private pool and my stomach-bug, I still wonder, and it has made me more disinclined to use any pool that isn't tested on a regular basis.)
At my local pool, I was really struck by the expertise and rapid-response of the lifeguards on duty when, one day, a swimmer got into difficulty. It made me even more aware of how, diabetic or not, it's safer to swim in a lifeguarded pool. I like the idea of wild swimming and sea-swimming, but personally, I'm not a sufficiently strong swimmer to risk it without company, and being diabetic, I get my swimming exercise where there are lifeguards.
