Going for a swim after eating does not pose any particular danger if you are in good health. Only discomfort may be felt. This is why it is advisable to wet your stomach and neck before entering the water.
And if during the digestion, the temperature of our body increases to favor it. Rest assured, this temperature rise is minimal. And so there is no risk ofhydrocution.
Be careful, however, in the event of a copious and watered meal in fragile people who can not bear the bath well!