Swimming is a fun sport and an excellent workout that can help you lose weight by burning several calories while having fun.
Swimming works several different muscle groups and the cardiovascular system which benefits your health in other ways too and it's a good way to cool off in the summer.
So if you swim everyday or often enough then you can lose a a lot of weight and to lose enough weight you should swim at least 30 minutes everyday but of course the more you swim the more calories you'll burn off.
And the more calories you burn off the more weight you lose.