swimming and weight loss

Someone told me that you can't lose weight from swimming but couldn't explain further.  I don't think it makes any sense-- you're moving, how can you not be burning calories?  My friend responded, "Oh yes! I've heard that too!" and even though it seems ridiculous, I'm worried. 

I often swim a kilometer and a half in 40 minutes and used to do two and a half in a session. Did she think that because I'm obese, I just splash around and call that swimming?

Is there any truth to this?

View the original article here