I heard you can't lose weight by swimming, is that true?
I can only speak from personal experience as I have not researched this particular concern. However, being an avid swimmer and weight loser, I do have a lot of thoughts on this.
No, I never could lose pounds swimming. It's great for maintaining, however.
I lost my necessary pounds by following a food plan, prayerful surrender, and by doing joyous dance aerobics for about a year. Then, at 32, after a lifetime of avoiding swimming due to fear and embarrassment, I enrolled in a beginners class. I put my fear aside and took the plunge. After a few lessons I was totally immersed and delighted in water recreation.
It changed my life--freeing me in ways that still bring a smile to my face. But I didn't lose a pound in two years of swimming regularly - one hour, twice a week. My theory is the body needs heat to burn fat and the coolness of water affects the process.
So, what to recommend? A program of aerobic movement or yoga twice or thrice a week for weight loss (and fun) combined with swimming (aqua jogging, stretching or ballet, laps, games, etc.) for the sheer joy of it.