Its cardio, and cardio is good for everyone no matter whether its for losing weight or generally. Cardiovascular exercise uses all the major muscle groups of the arms, trunk and legs. Any cardio can help with weight loss in a sense because your burning more than your consuming but mostly helps to make you a stronger and fitter person. You get better strength and endurance from swimming and you get fitter by the day. And also I think its a fun form of sport! Its better to move than to do none at all!
swimming is the best all round exercise as missammi says swimming is better than doing nothing
walking is also a good free exercise walk to work if possible if not get of the bus a couple of stops earlier.
Take the stairs instead of the lift
take the dog for an extra walk if you have one.