Swimming with Dexcom

I found some info online that helps: “If the energy cost of the jog is below 80% of your maximum capacity to use oxygen, then your BG may fall during the activity because more glucose enters the muscle than is released from the liver. Note the key role of exercise intensity: If the jog is above 80% of your maximum capacity to use oxygen, the CRH level greatly rises, stimulating an even higher rate of glucose secretion from the liver with BG rising during the exercise rather than falling.
Several recently published papers have observed this 80% intensity threshold. In fact, BG rises even in non-diabetics with exercise at this level of intensity! However, the non-diabetic pancreas quickly releases more insulin to match the rise in BG and soon BG returns to normal.
So, if you sometimes find that exercise causes your BG to rise rather than fall, it may be that the exercise is strenuous enough to hit or surpass the 80% mark. By reducing the intensity of the activity, you may find that your BG falls.”
https://www.diabeteshealth.com/exercise-why-is-my-bg-so-variable-hormones-supply-the-answer/