Snorkel and swimming workout

[underjeep]

Quick little stats:
-160 / 5'9"
-working out 2 years focusing on muscle building
-goal: i want abs

I'm growing bored of my cardio routine which is usually treadmill and steps and want to start swimming. I'm a really inefficient and bad swimmer but for the purposes of working out muscle groups I don't think it matters how slowly you swim as long as your muscle groups are getting a workout and you are getting tired.
I have difficulty breathing during swimming, my question is would a snorkel help me workout better in the same amount of time so I don't have to worry about oxygen limiting my gains? Is it normal for people to swim with a snorkel in a swimming pool? I can do everything except breath while swimming.