Exercise... after a very very long time!

It is probably a good idea to start with a slightly higher BG perhaps by eating a small snack.
And take it easy the first few times.
Then test more often than usual for the next 24 hours.

We are all different and react differently to exercise so there is a bit of trial and error to find out how it affects you.

Maybe best to start swimming with no active bolus, taking it easy at first is very good advice as is raising your BG, myself using Lantus can see a BG drop from 11 to 4.5 swimming for 40 minutes some days, other days less of a drop and the odd post swim hypo on others.

As said above, everybody's different, you will run the risk of the odd hypo and high swing, but the benefits from swimming, in my opinion at least, outweigh the manageable hazards hands down.

As long as you enjoy it!