When swimming people burn between 590 and 704 calories per hour of swimming.
But it also depends on the persons weight and the speed that they swim at.
A person that weighs in at around 155 pounds will burn 704 calories if they swim fast for 1 hour but if that same person swims slower they will burn around 493 calories swimming.
Now a person who weighs in at around 130 pounds and swims fast will burn 590 calories but if that same person swam slower they would only burn off around 493 calories.