Does weekends swimming will help to reduce weight, how much weight reduce if we do in weekends?

Swimming is probably the best exercise to do to lose weight, but to lose weight effectively you can't rely only on exercise, you should decrease your intake of food also.
Stopping the exercise will make you gain weight, can you replace it with something else?
Swimming hard for an hour will burn as many as 750 calories, that sounds a lot but if you are only swimming at weekends it will not make a huge difference to your weight.