Diets don't seem to work for me and I always end up going back to counting calories. If you are counting calories too, My Fitness Pal is a great way to keep track (You can add their app to your phone). And don't forget to include calories burned. There are lots of calculators you can use.
Glamour Fitness Calculator
My Fitness Pal Calculator
Even moderate swimming burns over 300 calories for 30 minutes.